Methods for continuously placing filaments within hydraulically settable compositions being extruded into articles of manufacture

ABSTRACT

Methods and apparatus for continuously extruding a hydraulically settable mixture and simultaneously placing continuous filaments within the extruding mixture to yield articles having a filament-reinforced, hydraulically settable matrix. The filaments can be placed within the mixtures in a parallel configuration, a helical configuration, or combinations thereof, in order to yield an article having the desired properties of, e.g., tensile strength, flexural strength, hoop strength, burst strength, toughness, and elongation ability. The desired properties of the hydraulically settable mixture, as well as of the cured hydraulically settable matrix of the hardened article, may also be adjusted by including varying amounts and types of aggregates, discontinuous fibers, binders, rheology-modifying agents, dispersants, or other admixtures within the hydraulically settable mixture. Optimizing the particle packing density while including a deficiency of water yields a hydraulically settable mixture which will flow when an extrusion pressure is applied but be form stable upon being extruded.

RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 08/255,344, entitled "Methods For The Extrusion OfNovel, Highly Plastic And Moldable Hydraulically Settable Compositions,"and filed Jun. 7, 1994, in the names of Per Just Andersen, Ph.D., andSimon K. Hodson. This application is also a continuation-in-part ofco-pending U.S. patent application Ser. No. 08/019,151, entitled"Cementitious Materials For Use in Packaging Containers and TheirMethods Of Manufacture," and filed Feb. 17, 1993, in the names of PerJust Andersen, Ph.D., and Simon K. Hodson, now issued as U.S. Pat. No.5,453,310. This application is also a continuation-in-part of co-pendingU.S. patent application Ser. No. 08/095,662, entitled "HydraulicallySettable Containers And Other Articles For Storing, Dispensing, AndPackaging Food And Beverages And Methods For Their Manufacture," andfiled Jul. 21, 1993, in the names of Per Just Andersen, Ph.D., and SimonK. Hodson, now issued as U.S. Pat. No. 5,385,764. This application isalso a continuation-in-part of co-pending U.S. patent application Ser.No. 08/101,500, entitled "Methods And Apparatus For ManufacturingMoldable Hydraulically Settable Sheets Used In Making Containers,Printed Materials, And Other Objects," and filed Aug. 3, 1993, in thenames of Per Just Andersen, Ph.D., and Simon K. Hodson. This applicationis also a continuation-in-part of co-pending U.S. patent applicationSer. No. 08/109,100, entitled "Design Optimized Compositions AndProcesses For Microstructurally Engineering Cementitious Mixtures," andfiled Aug. 18, 1993, in the names of Per Just Andersen, Ph.D. and SimonK. Hodson (now abandoned). Each of these applications is also acontinuation-in-part of co-pending U.S. patent application Ser. No.07/929,898, entitled "Cementitious Food And Beverage Storage,Dispensing, And Packaging Containers And The Methods Of ManufacturingSame," and filed Aug. 11, 1992, in the names of Per Just Andersen,Ph.D., and Simon K. Hodson (now abandoned). For purposes of disclosure,each of the foregoing applications is incorporated herein by specificreference.

BACKGROUND OF THE INVENTION The Field of the Invention

The present invention relates to methods and systems for manufacturingarticles of manufacture from hydraulically settable mixtures containingfilaments (i.e., continuous fibers). More particularly, the inventionrelates to methods and systems for extruding hydraulically settablemixtures into desired shapes or articles while simultaneously placingfilaments within the structural matrix of the extruded articles. Thehydraulically settable mixtures are microstructurally engineered to havetheological properties that render the mixtures highly extrudable underpressure and then form stable immediately after they have been extruded,even while in the green or unhardened state. The filaments within thehydraulically settable matrix of the extruded articles increase the,e.g., tensile strength, flexural strength, burst strength (in the caseof pipes or other hollow articles), elasticity modulus, and elongationand deflection before rupture of the extruded articles.

THE RELEVANT TECHNOLOGY

Hydraulically settable materials, such as those that contain ahydraulically settable binder like hydraulic cement or gypsum(hereinafter "hydraulically settable," "hydraulic," or "cementitious"compositions, materials, or mixtures), have been used for thousands ofyears to create useful, generally large, bulky structures that aredurable, strong, and relatively inexpensive. Hydraulic cement is ahydraulically settable binder derived from clay and limestone, whilegypsum is a naturally occurring mineral. Both are essentiallynondepletable.

Hydraulically settable materials are generally formed by mixing ahydraulically settable binder with water and usually some type ofaggregate to form a hydraulically settable mixture, which hardens into,e.g., concrete. Typically, a freshly mixed hydraulically settablemixture is fairly nonviscous, semi-fluid slurry, capable of being mixedand formed by hand. Because of its fluid-like nature, a hydraulicallysettable mixture is generally shaped by being poured into a mold, workedto eliminate large air pockets, and allowed to harden.

Due to the high level of fluidity required for typical hydraulicallysettable mixtures to have adequate workability, the uses of concrete andother hydraulically settable materials have been limited to mainlysimple shapes which are generally large, heavy, and bulky, and whichrequire mechanical forces to retain their shape for an extended periodof time until sufficient hardening of the material has occurred. Anotheraspect of traditional hydraulically settable mixtures or slurries isthat they have little or no form-stability and are usually molded intothe final form by pouring the mixture into a space having externallysupported boundaries or walls. The problem of low form-stability isexacerbated by the lengthy curing and hardening times of most concretes.It may take days for most cementitious mixtures to have enough strengthto be demolded without being harmed, and weeks of wet curing to avoiddefects in the structural matrix.

The uses of hydraulically settable materials have also been limited bythe strength properties of concrete, namely, the high ratio ofcompressive strength to tensile strength, which is usually about 10:1.Nevertheless, the strength limitations of concrete can often be overcomeby simply molding massive structures of concrete having enormous size.This is possible because of the extremely low cost of most concretes.The tensile and flexural strengths of such massive structures can beimproved by extensive use of large metal reinforcing bars, or "rebar".Similarly, on a more "microscopic" level, the incorporation ofrelatively small, chopped or discontinuous fibers within thehydraulically settable structural matrix can greatly increase the, e.g.,strength and elongation properties and toughness of the hardenedhydraulically settable article. Through thorough mixing of the fiberswithin the green hydraulically settable mixture it is possible to obtaingood fiber to hydraulically settable matrix interaction with a minimumof interior defects within the matrix.

Others have attempted to introduce continuous fibers into thecementitious structural matrix in the form of mats, cords, wire forms,yarns, or filaments, but with only moderate success in producingsignificantly stronger and tougher articles. One such method is the"lay-up technique" in which the appropriate source of continuous fibers(such as mats, or cords) are placed into the desired configuration,usually within a mold or form, after which an appropriate hydraulicallysettable mixture is poured into the mold or form and worked to permeateand encapsulate the continuous fibers. However, because of the generalinability to fully consolidate the hydraulically settable mixture withinthe spaces defined by the continuous fibers, particularly those in whichthe continuous fibers or filaments are relatively close together, thehardened hydraulically settable structure will usually have asignificant quantity or volume of unwanted voids or defects within thehydraulically settable matrix. In many cases, it has proven to beimpossible to fully remove the unwanted voids and consolidate thehydraulically settable mixture even by applying pressure to or vibratingthe continuous fiber-filled hydraulically settable material. Thegenerally poor condition and low strength of the cementitious mixturesimpregnated with continuous fibers by means of the lay-up method oftenoffsets whatever strength properties the continuous fibers were intendedto impart to the cementitious mixture.

In an effort to improve the placement of continuous filaments within acementitious mixture, some have used conventional filament windingtechniques in which continuous filaments are wrapped around and into apreviously molded, green cementitious mixture supported and rotated by amandrel. See F. Strabo et al., "Nye Formgivningsmetoder til Fiberbeton,"Byggeteknik Institut, April 1987 (F. Strabo et al., "New Design Methodsfor Fiber Concrete," Danish Technological Institute, April 1987). Oneadvantage of this method was that it allowed for the placement ofgreatly varying concentrations of continuous filaments within acementitious material, and also along a variety of desired anglesrelative to the longitudinal axis of the pipe or cylinder being filamentwound. It was even possible to place helically oriented andcriss-crossed filaments using the conventional filament windingtechnique. Varying the concentration and/or orientation of thecontinuous filaments would be expected to greatly affect the strength,toughness, and other desired properties of the final cured cementitiousarticle.

In general, filament winding is used to increase the hoop or burststrength of hollow tubes or pipes, which greatly increases the amount ofinternal pressure that such tubes or pipes can withstand before ruptureor failure. The effect of filament winding on burst strength is enhancedif the filaments are placed in a manner so that they criss-cross oroverlap, have a relatively large angle of offset relative to thelongitudinal axis of the pipe or tube, and have a larger relativeconcentration vis-a-vis the material into which they are placed.

While the filament winding method set forth in Strabo et al.significantly improved the quality of the final cementitious product,the method was time consuming and costly, and did not provide aneconomically viable method for manufacturing filament wound cementitiousmaterials on a grand scale. In addition, the surface quality of suchfilament wound cementitious materials tended to be rather poor due tothe effect of the filament's cutting through the surface and interior ofthe green cementitious material. Effective consolidation of thecementitious material into which filaments had been placed oftenrequired smoothing over the surface by hand or through other timeconsuming procedures.

It is readily apparent that neither the lay-up technique nor thetraditional filament winding processes provide a method for thecontinuous formation of hydraulically settable materials intoinexpensive, mass-producible articles. As set forth more fully inco-pending U.S. patent application Ser. No. 08/255,344, entitled"Methods For The Extrusion Of Novel, Highly Plastic And MoldableHydraulically Settable Compositions," and filed Jun. 7, 1994, in thenames of Per Just Andersen, Ph.D., and Simon K. Hodson (hereinafter the"Andersen-Hodson Extrusion Technology"), some have attempted to extrudecementitious materials in an effort to continuously produce cementitiousarticles such as, e.g., pipes or rods. See U.S. Pat. Nos. 3,857,715 toHumphrey and 5,588,443 to Bache et al. Nevertheless, although suchpatents claim that the cementitious materials disclosed therein can beextruded using traditional extruder and die apparatus, such extrusionefforts were performed in the laboratory and only under experimentalconditions. To date, there are no workable processes or materials forcontinuously extruding a cementitious mixture except into fiat slabs orboard-like sheets. See, e.g., U.S. Pat. Nos. 5,047,086 to Hayakawa etal., 4,613,627 to Sherman et al., and 4,655,981 to Nielsen et al.Moreover, the materials set forth in the foregoing patents lack formstability and are, therefore, suitable only for extrusion into fiatslabs or thick sheets that are supported by a conveyer belt or platformuntil sufficiently cured.

Because of the tradeoff between workability (and extrudability) andform-stability, cementitious materials which are "extruded" horizontallyaccording to conventional methods generally must have a wall thicknessof about 25% of the cavity cross-section in the case of hollow objects(e.g., pipe), although vertically extruded objects can have a wallthickness to cavity cross-section up to about 1:16.

Even when fully cured, typical cementitious materials, even thosedisclosed in the previously mentioned extrusion patents, have relativelylow tensile and flexural strengths compared to other materials such aspaper, metal, or plastic. Moreover, these patents do not teach how onemight continuously reinforce the extruded cementitious articles witheither parallel or wound filaments. Consequently, even such extrudablematerials have limited use in mainly large, bulky, heavy-weight objects.Therefore, it would be a tremendous advancement in the art if a widervariety of articles having complex shapes or highly critical tolerancescould be manufactured from hydraulically settable materials,particularly in light of the extremely low cost of hydraulicallysettable materials compared to most other materials. It would be an evengreater improvement in the art if such hydraulically settable articlescould be manufactured with continuous filaments to increase the strengthand toughness of the articles so that they could substitute forconventional materials such as plastic, metal, wood, or clay presentlyused to manufacture, e.g., pipes, window frames, two-by-fours, moldings,rods, etc.

Due to a growing awareness of the environmental harm caused by themassive use of plastic, metal, and wood to manufacture enormousquantities of both long-lasting structural components, as well asdisposable items, there has been an acute need to find environmentallysound substitutes for such materials. One such environmentally soundsubstitute would be hydraulically settable materials. In spite of suchpressures and long-felt need, the technology simply has not previouslyexisted for the economically feasible mass-production of hydraulicallysettable materials which could be substituted for plastic, metal, orwood in making a huge variety of articles.

Hydraulically settable materials are environmentally sound because theyessentially include aggregates consisting of natural geologic materials,such as sand and clay, which are bound together by the reaction productsof a hydraulically settable binder and water, which is also essentially"rocklike" from a structural and, especially, chemical, viewpoint.Hydraulically settable materials have essentially the same chemical andstructural composition as the earth into which such materials mighteventually be disposed.

In addition, plastic, metal, and wood are far more expensive thantypical hydraulically settable (including cementitious) materials.Because no rational business would ignore the economic benefit whichwould necessarily accrue from the substitution of radically cheaperhydraulically settable materials for plastic, metal, or wood materials,the failure to do so can only be explained by a marked absence ofavailable technology to make the substitution.

Based on the foregoing, it would be an advancement in the art to providecompositions, methods, and apparatus that would allow for thesimultaneous placement of filaments during the extrusion ofhydraulically settable materials into articles and shapes which haveheretofore been impossible because of the inherent strength andmoldability limitations of presently known hydraulically settablecompositions.

It would yet be an advancement in the art to provide compositions,methods, and apparatus for the extrusion of and placement of filamentswithin hydraulically settable articles having an increased tensilestrength to compressive strength ratio compared to conventionalhydraulically settable materials.

It would yet be a tremendous advancement in the art to providecompositions, methods, and apparatus which would result in the abilityto continuously extrude, and simultaneously place filaments within, ahydraulically settable mixture such that the extruded article or shapewould be immediately form stable (i.e., be strong enough to maintain itsshape without external support) in the green state upon exiting theextruder die.

It would be a further improvement in the art if such composition,methods, and apparatus allowed for the continuous placement of filamentshaving a variety of desired concentrations within an extrudinghydraulically settable mixture.

In addition, it would be a tremendous advancement in the art to providefor the placement of continuous filaments within an extrudinghydraulically settable mixture at a variety of different orientations orangles relative to the longitudinal axis of the extruded article.

It would yet be a major improvement in the art if such compositions,methods, and apparatus provided for the ability to extrude form stablepipes and tubes having substantially increased hoop or burst strength.

It would further be a significant improvement in the art if suchcompositions, methods, and apparatus provided for the effectiveconsolidation or compaction of the hydraulically settable mixture aroundand through the continuously placed filaments in order to minimize theamount and volume of internal voids or defects and thereby yield ahardened hydraulically settable structure matrix that is substantiallyuniform and of consistently high strength.

It would yet be an improvement in the art if such compositions, methods,and apparatus provided for extruded hydraulically settable articles intowhich filaments could be continuously placed that had superior surfaceproperties and greatly reduced surface defects compared to prior artmethods for filament winding cementitious materials.

Still, it would be an advancement in the art if such compositions,methods, and apparatus yielded a variety of thin-walled hydraulicallysettable articles, including articles that require highly criticaltolerances or dimensional preciseness.

It would be a tremendous advancement in the art to provide compositions,methods, and apparatus which could be used to extrude, and placecontinuous filaments within, hydraulically settable articles that couldsubstitute for articles presently manufactured from conventionalmaterials such as plastic, clay, metal, or wood.

It would be an advancement in the art if such hydraulically settablecompositions had a rheology and a plastic-like behavior similar to claysuch that such compositions could be extruded using a clay extruder.

From a practical point of view, it would be a significant improvement ifsuch compositions, methods, and apparatus could be used to continuouslymanufacture a large variety of hydraulically settable articles at a costand at production rates (i.e., high volume or quantity) comparable oreven superior to the cost of manufacturing such articles from plastic,clay, metal, or wood.

Such compositions, methods, and apparatus are disclosed and claimedherein.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention encompasses novel hydraulically settablecompositions, methods, and apparatus used in the extrusion of and thesimultaneous placement of continuous filaments within hydraulicallysettable compositions to form a large variety of articles. Suchfilaments can be longitudinally oriented, wound at an angle relative tothe longitudinal axis, or a combination of the two. The preferredhydraulically settable compositions can generally be described asmulti-component, multi-scale, fiber-reinforced, micro-composites. Bycarefully incorporating a variety of different materials (includinghydraulically settable binders, inorganic aggregates, rheology-modifyingagents, and fibers) capable of imparting discrete yet synergisticallyrelated properties, a unique class or range of micro-composites havingremarkable properties of strength, toughness, environmental soundness,mass-producibility, and low cost can be created.

Such compositions can be extruded into a variety of shapes, ranging fromthe very simple to articles having highly critical tolerances and thinwalls. Because of the continuous nature of both the extrusion andfilament placement processes, such articles can be produced in a verycost-effective and economical manner. Moreover, the hydraulicallysettable materials of the present invention are environmentally neutraland comprise materials that have essentially the same qualities andcharacteristics as the earth.

Using a microstructural engineering approach, one can design into ahydraulically settable mixture the desired properties of rheology(including workability, yield stress, viscosity, and green strength) andfinal cured strength. In addition, properties such as high particlepacking density, toughness, tensile strength, and elongation can also bedesigned into the mixture beforehand. In addition, by placing filamentshaving the desired properties of strength and flexibility into an almostendless variety of orientations and concentrations one can continuouslymanufacture reinforced articles having even greater strength,durability, flexibility, and toughness.

The usual problems inherent in typical hydraulically settable mixtures,namely the tradeoff between good workability and high green strength,are solved by creating a hydraulically settable mixture having arelatively high yield stress and an apparently low viscosity,particularly when exposed to higher pressure and shear during theextrusion process. By this means the present invention makes possiblethe ability to have a high degree of workability during the extrusionprocess and then immediate form-stability thereafter.

The extrudability and high green strength (i.e., form-stability) of thehydraulically settable mixtures of the present invention are attainedthrough a combination of the heretofore perceived nonanalogousproperties of particle packing optimization and water deficiency tocreate a relatively stiff material with high yield stress, but which hashigh workability when subjected to the increased pressures and shearrates associated with extrusion. By choosing aggregates selected to havevarying but carefully chosen diameters, particle size distribution("PSD"), and packing density, it is possible to reduce the amount ofinterstitial space between the particles by filling the spaces betweenthe larger particles with smaller particles, and in turn filling thespaces formed by the smaller particles by yet smaller particles. In thisway, it is possible to achieve particle packing densities in the rangefrom about 65% to even as high as about 99%. That is, the volume of thedry hydraulically settable mixture will include from about 65% to about99% solid material, and only from about 35% to as low as about 1%interstitial space or voids.

By carefully controlling how much water is added to the hydraulicallysettable mixture, one can create a mixture having a carefully chosendegree of "water deficiency." (As discussed in greater detail below, itshould be understood that water is added to a hydraulically settablemixture for essentially two reasons: (1) to chemically react with (or"hydrate") the hydraulically settable binder and (2) to fill the voidsbetween the particles in order to reduce the friction between theparticles and lubricate them in order to give the mixture adequateplasticity and cohesion. If the amount of water is deficient, there willbe greater friction between the particles, thereby resulting in astiffer material. Depending on the amount of water or other additives(such as dispersants, which can be added to lubricate or disperse theparticles), one skilled in the art can carefully control the rheology inorder to create the desired level of workability under pressure.

It should be understood that a mixture having greater packing densitywill require much less water to fill the interstitial voids.Consequently, the amount of water added to create a desired level ofwater deficiency is preferably determined before the water is added, theamount of water being based primarily upon the particle packingefficiency and the anticipated compression of the extrusion process.

Once a suitable hydraulically settable mixture has been created, it isplaced in an extruder and then subjected to pressure. The resultingcompression increases the packing density by forcing the particlestogether, which in turn decreases the volume of interstitial spacebetween the individual particles of the mixture. This decreases the"effective" level of water deficiency, which increases the amount ofwater available to lubricate the particles (as well as to lubricate themovement of the hydraulically settable mixture through the extruderdie), whereupon the hydraulically settable mixture has greaterworkability and is able to flow. In addition, compressing the mixtureduring extrusion also creates a thin film of water between the extruderdie and the mixture, which lubricates the surface between the die andmixture. The extruder die may also be heated in order to create a steam"cushion" or barrier between the extruded hydraulically settable mixtureand the extruder die, thereby reducing the friction and increasing theease of extrusion. Thereafter, the internally formed capillaries ormenisci caused by compressing the mixture creates internal cohesionforces that give the mixture improved form-stability after extrusion.

The high level of workability and flowability of the mixture while underpressure allows it to be extruded through an orifice of an extruder dieinto the desired article or shape. The ability of the hydraulicallysettable mixture to be extruded and have good form-stability may beaccomplished in one of two ways. First, because most of thehydraulically settable mixtures of the present invention approximatelybehave as a Bingham fluid, or pseudoplastic body, the viscosity of themixture will decrease as the critical shear rate in the form of appliedpressure is exceeded. In other words, the hydraulically settablemixtures of the present invention usually experience "shear thinning" asthe pressure (and hence the shear) is increased, such as by using anextruder capable of applying high pressure. Hence, by applying highpressures (and creating the attendant shear), most hydraulicallysettable mixtures of the present invention can be extruded.

Instead of, or in addition to the application of high pressure, it mayalso be advantageous to design a hydraulically settable mixture that hasthe lowest possible ratio of viscosity to yield stress. As the viscosityis lowered, the amount of stress above the yield stress of the materialsnecessary to cause the mixture to flow decreases. This strategy isespecially useful where lower pressure extrusion is desired.

Upon being extruded, the hydraulically settable mixture will no longerbe exposed to the compressive and shear forces of the extruder, and themixture will then attain greater stiffness, viscosity, cohesion, formstability, and green strength. The amount of green strength achieved bythe compositions, methods, and apparatus of the present invention farexceeds that which has been obtained using previous cementitiouscompositions, methods, and apparatus.

The hydraulically settable compositions of the present invention mayalso include other components besides a hydraulically settable binder,water, and aggregates such as rheology-modifying agents, dispersants,and fibers. Rheology-modifying agents can be added to increase the yieldstress, cohesive strength, and plastic-like behavior of thehydraulically settable mixture, while dispersants can be added in orderto obtain a mixture having similar flow properties while including lesswater. Fibers are usually added to increase the toughness and tensile,flexural and, sometimes, even the compressive strength of the finalcured product.

More particularly, rheology-modifying agents increase the "plastic-like"behavior, or the ability of the mixture to retain its shape when moldedor extruded. Suitable rheology-modifying agents include a variety ofcellulose-, starch-, and protein-based materials, which can be ionic ornonionic, and which act by gelating the water and by bridging theindividual hydraulically settable binder particles and other particleswithin the hydraulically settable mixture together. By increasing the"plastic-like" consistency of the hydraulically settable mixture, therheology-modifying agent also increases the ability to extrude anarticle having high form-stability. (Gypsum hemihydrate may also beadded in order to increase the form-stability due to its rapid reactionwith water, thereby reducing the amount of capillary water present inthe hydraulically settable mixture in a short period of time. In thisway, gypsum hemihydrate may act as a rheology-modifying agent in somecases.)

Dispersants, on the other hand, act to decrease the viscosity and yieldstress of the mixture by dispersing the individual hydraulicallysettable binder particles. This allows for the use of less water whilemaintaining adequate levels of workability, which allows for greaterwater deficiency. Suitable dispersants include any material which can beadsorbed onto the surface of the hydraulically settable binder particlesand which act to disperse the particles, usually by creating a negativeelectrical charge on the particle surface or into the near colloiddouble layer. Fillers such as kaolin, mica, calcium carbonate, orbentonite also become highly dispersed by the use of dispersants.

However, in the case where both a dispersant and a rheology-modifyingagent are used, it will usually be advantageous to add the dispersantfirst and the rheology-modifying agent second in order to obtain thebeneficial effects of each. Otherwise, if the rheology-modifying agentis first adsorbed by the binder particles, it will form a protectivecolloid, which will greatly inhibit the adsorption of the dispersant bythe particles, thereby limiting the dispersing effect of the dispersantwithin the hydraulically settable mixture.

In addition to adding aggregates having various diameters, shapes,sizes, and properties (e.g., specific gravity, bulk density,morphology), it might be desired to include aggregates having differentstrength and insulation properties. In this way, the hydraulicallysettable mixture can be optimized both from the standpoint of thedesired rheology or flow properties useful in the extrusion process aswell as the final properties of the cured material.

Finally, the primary novel feature of the present invention is theability to introduce filaments or continuous fibers into the structuralmatrix of the extruded article during the extrusion process.Introduction of filaments during the extrusion process involves placingthe filaments into the mixture, which encases and draws the filaments inthe hydraulically settable mixture along in the extrusion direction. Thehydraulically settable mixture becomes consolidated or compacted as aresult of the internal pressure applied to the mixture during theextrusion process, thereby minimizing the amount and volume of internalvoids or defects within the mixture and maximizing the interface betweenthe filaments and the hydraulically settable mixture. Increasing theinterface between the filaments and matrix helps to more securely anchorthe filaments within the hydraulically settable structural matrix.

Different embodiments of the apparatus for continuously placingfilaments within the extruding hydraulically settable mixture permit thefilaments to be placed in a variety of configurations or orientations.These include parallel configuration, helical configuration, criss-crossconfiguration, or combinations of these configurations. In a "parallelconfiguration" the filaments are generally coaxial to the longitudinalaxis, or extrusion direction, of the hydraulically settable article.Conversely, in the "helical configuration" and "criss-crossconfiguration" (which is merely a variation of the helicalconfiguration), the filaments are offset from the longitudinal axis,usually at an angle α of at least about 5° up to a maximum of about 90°,which may be referred to herein as the "offset angle", "winding angle"or "spiral angle". (Depending on the direction of rotation of thefilament placing means, i.e., clockwise or counterclockwise, angle α caneither be positive or negative but will not have a magnitude greaterthan 90°, an angle of 91° being identical to an angle of -89°.)

By varying the concentration and/or angle of orientation of thefilaments placed within the extruded hydraulically settable articles ofthe present invention, a wide variety of strength, elongation, andtoughness properties can be attained. Filaments having a lower windingangle will generally define an elliptical cross section of the pipe orcylinder into which they are placed. As the winding angle increases to90°, the filaments will tend to define an ellipse of diminishingcross-width. At an angle of 90°, the filaments will define a circularcross section. Assuming that the article being extruded is a pipe,cylinder, or other article having a generally circular cross-section, itwill have a radius that is generally perpendicular to the longitudinalaxis. For purposes of defining the direction and magnitude of thestrength imparted by the filaments, it would be useful to define thestrength imparted by the filaments as having vector componentscorresponding to the longitudinal axis and radius, respectively.Whenever a filament has an angle of offset greater than 0° but less than90°, the filament will have both a longitudinal vector component and aradial vector component. In filaments having a winding angle less than45°, the longitudinal strength vector would be expected to generallyexceed the radial strength vector. Similarly, in filaments having awinding angle greater than 45°, the radial strength vector would beexpected to generally exceed the longitudinal strength vector.

In general, more longitudinally oriented filaments having a greaterlongitudinal strength vector will tend to increase the tensile strengthof the hydraulically settable article in the longitudinal, orlength-wise, direction. Conversely, filaments having a greater angle ofoffset relative to the longitudinal axis, i.e., those having a greaterradial strength vector, will instead tend to increase thecircumferential strength (otherwise known as hoop or burst strength inthe case of a pipe or other hollow structure). A mixture of filamentshaving both higher and lower angles of offset can be used in order toimpart each of these properties.

The apparatus comprises means for continuously placing filaments withinan extruding hydraulically settable mixture which are in directcommunication with a filament placement chamber, which is an interiorchamber of an extruder. The apparatus further comprises means forstoring and continuously providing filaments to at least one placingmeans.

The placing means place the filaments at or below the surface of thehydraulically settable structural matrix and the hydraulically settablemixture draws the filaments forward as the mixture advances. The placingmeans can be a rotatable placing means which rotate either clockwise orcounterclockwise around the filament placement chamber by means forrotating the placing means, thereby winding the filaments in a helicalconfiguration extending within the article along the same axis as theextrusion direction. The placing means can also be a fixed placing meanswhich remains stationary to place the filaments in a parallelconfiguration. Operation of at least two placing means at differentspeeds or direction will yield an article having filaments of varyingangles of offset from the longitudinal axis.

Each placing means comprises means for receiving at least one filamentinto the placing means, means for channeling the received filamentthrough the placing means and means for inserting the filament into thefilament placement chamber. The means for inserting can have any shapecapable of positioning the filaments at or below the surface of thehydraulically settable structural matrix and can have varyingcross-sectional shapes. Example of a means for inserting include a nibend, a scoop end or a hollow needle which extend into the filamentplacement chamber from a channeling means.

The means for storing and continuously providing filaments to at leastone placing means comprises a filament dispenser, such as a spool. Themeans for storing and continuously providing filaments to at least oneplacing means further comprises at least one feeder ring which supportsat least one filament dispenser. The means for storing and continuouslyproviding filaments can rotate with the rotatable placing means orremain stationary for use with the fixed placing means. The filamentdispenser may also comprise tensioners to provide tension on thefilaments.

The placement level of the filaments within the hydraulically settablestructural matrix can be varied by varying the position of the placingmeans. The placement level can also be altered by selectively adjustingthe tension on the fibers by tensioners. In general, the greater thetension, the greater the depth of placement of the filament. Inaddition, the extrusion pressure and mixture rheology also affect theplacement of the filaments to some degree.

The angle α at which the filament is placed is a function of both theforward extrusion speed ("V_(e) "), as well as the rotational velocity("V_(r) ") of the placing means. In fact, the tangent of angle α isproportional to the ratio of the rotational velocity to the extrusionspeed (V_(r) /V_(e)). Therefore, all things being equal, the faster theextrusion speed, the lower the winding angle of the filaments.Conversely, the greater the magnitude of the rotational velocity of theplacing means the greater the magnitude of the winding angle of thefilaments. The concentration of filaments within the hydraulicallysettable matrix of the extruded article is directly proportional to boththe number of filaments, as well as the average angle α of thefilaments. As both the number and average angle α of the filamentsincreases, so does the concentration. The greater the concentration offilaments, the less space there is between the individual filamentstrands. This results in a greater and more uniform effect imparted bythe filaments to the hydraulically settable matrix of the extrudedarticle. In general, smaller diameter fibers more closely spacedtogether will tend to more uniformly impart the desired properties of,e.g., strength, flexibility, and toughness compared to larger diameterfibers.

Finally, depending on their chemical makeup, the filaments themselvescan have greatly varying tensile and shear strengths, as well asflexibility and the ability to elongate. Such properties are alsoaffected by the diameter of the filaments, or whether they consist of asingle strand or a groups of strands twisted or otherwise joinedtogether to form a single filament unit.

Using the compositions, methods, and apparatus described above, it ispossible to extrude a wide variety of differently shaped articles havingcontinuous filaments dispersed within the hydraulically settable matrixof the articles. Such extruded articles include generally square,rectangular, cylindrical, or elliptical rods or bars, boards, "I-beams,""two-by-fours," simple multicellular structures, pipes, tubes, or otherhollow structures, window frames, bricks, or roofing tiles. Sucharticles benefit from the internal placement of continuous filamentswithin a highly consolidated and compacted hydraulically settablematrix, while maintaining highly critical tolerances where needed.

Such articles have properties which are similar, and even superior, tosimilar articles made from other materials such as plastic, wood, clay,or metal. However, hydraulically settable materials have the advantagein that they usually cost far less compared to these other materials. Inaddition, the hydraulically settable articles made according to thepresent invention are generally more environmentally neutral compared toconventional materials in present production.

From the foregoing, it will be appreciated that an important object andfeature of the present invention is to provide compositions, methods,and apparatus that allow for the simultaneous placement of filamentsduring the extrusion of hydraulically settable materials into articlesand shapes which have heretofore been impossible because of the inherentstrength and moldability limitations of presently known hydraulicallysettable compositions.

It is another object and feature to provide compositions, methods, andapparatus for the extrusion of and placement of filaments withinhydraulically settable articles having an increased tensile strength tocompressive strength ratio compared to conventional hydraulicallysettable materials.

Another object and feature is that such compositions, methods, andapparatus result in the ability to continuously extrude, andsimultaneously place filaments within, a hydraulically settable mixturesuch that the extruded article or shape is immediately form stable(i.e., is strong enough to maintain its shape without external support)in the green state upon exiting the extruder die.

Yet a further object and feature is that such composition, methods, andapparatus allow for the continuous placement of filaments having a widevariety of concentrations within an extruding hydraulically settablemixture.

Another object and feature is to provide for the placement of continuousfilaments within an extruding hydraulically settable mixture at avariety of different orientations or angles relative to the longitudinalaxis of the extruded article.

Yet another object and feature is that such compositions, methods, andapparatus yield extruded, form stable pipes and tubes havingsubstantially increased hoop or burst strength.

Still, a further object and feature of the present invention is toprovide compositions, methods, and apparatus which result in theeffective consolidation or compaction of the hydraulically settablemixture around and through the continuously placed filaments in order tominimize the amount and volume of internal voids or defects and therebyyield a hardened hydraulically settable structure matrix that issubstantially uniform and of consistently high strength.

In addition, an object and feature is that such compositions, methods,and apparatus yield extruded hydraulically settable articles into whichfilaments have been continuously placed that have superior surfaceproperties and greatly reduced surface defects compared to prior artmethods for filament winding cementitious materials.

Yet another object and feature is that such compositions, methods, andapparatus yield a variety of thin-walled hydraulically settablearticles, including articles that require highly critical tolerances ordimensional preciseness.

A further object and feature is to provide compositions, methods, andapparatus that can be used to extrude, and place continuous filamentswithin, hydraulically settable articles that can be substituted forarticles presently manufactured from conventional materials such asplastic, clay, metal, or wood.

Another object and feature of the present invention is to providehydraulically settable compositions that have a rheology and aplastic-like behavior similar to clay such that such compositions can beextruded using a clay extruder.

Still, another object and feature is to provide compositions, methods,and apparatus that can be used to continuously manufacture a largevariety of hydraulically settable articles at a cost and at productionrates (i.e., high volume or quantity) comparable or even superior to thecost of manufacturing such articles from plastic, clay, metal, or wood.

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto a specific embodiment thereof, which is illustrated in the appendeddrawings. Understanding that these drawings depict only a typicalembodiment of the invention and are not, therefore, to be consideredlimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a greatly enlarged elevational cross-section view of thearrangement of particles within a hydraulically settable mixture havinga moderately high natural particle packing density of 70%;

FIG. 2 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 1, together with a corresponding graphquantifying the volume occupied by the particles and the volume occupiedby the interstitial voids between the particles;

FIG. 3 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 1 to which a quantity of water equaling thevolume of interstitial voids has been added, together with acorresponding graph quantifying the volume occupied by the particles andthe volume occupied by the water between the particles;

FIG. 4 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 1 to which a quantity of water less than thevolume of interstitial voids has been added to form a water deficientmixture, together with a corresponding graph quantifying the volumeoccupied by the particles, the volume occupied by the water between theparticles, and the volume occupied by the interstitial voids that yetremain between the particles;

FIG. 5 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 4 upon which a compressive force (i.e.,pressure) has been applied sufficient to force the particles into a moreclosely packed arrangement, together with a corresponding graphquantifying the volume occupied by the particles, the volume occupied bythe water between the particles, and the lesser volume occupied by theinterstitial voids that yet remain between the particles;

FIG. 6 is a cross-section view of an auger extruder;

FIG. 7 is a cross-section view of a piston extruder;

FIG. 8 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates themixture being extruded towards the filaments;

FIG. 9 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates themixture encapsulating the filaments which are being placed in a helicalconfiguration as a rod is formed;

FIG. 10 is a transverse cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture taken along cutting planeline 10--10 of FIG. 9, which illustrates the placement of filaments by aplacing means having scoop ends;

FIG. 11 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates themixture encapsulating the filaments which are being placed in a parallelconfiguration by a placing means having scoop ends;

FIG. 12 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates themixture encapsulating the filaments which are being placed in a parallelconfiguration by a placing means having nib ends;

FIG. 13 is a transverse cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture taken along cutting planeline 13--13 of FIG. 12, which illustrates the placement of filaments bya placing means having nib ends;

FIG. 14 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates themixture encapsulating the filaments which are being placed in a parallelconfiguration by a placing means having hollow needles;

FIG. 15 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates theplacement of filaments in a criss-cross configuration by two sets ofrotatable placing means;

FIG. 16 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture, which illustrates theplacement of filaments in a parallel configuration by a set of fixedplacing means and in a criss-cross configuration by two sets ofrotatable placing means;

FIG. 17 is a perspective view of an apparatus with a cut-away view of anI-beam shaped filament placement chamber, which illustrates theformation of a hydraulically settable I-beam with filaments placed in aparallel configuration along the length of the I-beam;

FIG. 18 is a perspective view of an apparatus forming a hydraulicallysettable sheet with filaments placed in a parallel configuration alongthe length of the sheet;

FIG. 19 is a perspective view of an apparatus with a cut-away view of afilament placement chamber having a circular cross-section along itslength and a rectangular cross-section at the exit end of the filamentplacement chamber, which illustrates the formation of a hydraulicallysettable article having a rectangular cross-section with filamentsplaced in a helical configuration along the longitudinal axis of thearticle and filaments placed in parallel configuration in the cornersand the perimeter of the article;

FIG. 20 is a perspective view of an apparatus with a cut-away view of afilament placement chamber having a circular cross-section whichtranscends gradually along its length to having a square cross-sectionat the exit end of the filament placement chamber, and a mandrel isshown in the filament placement chamber that also transcends from havinga circular cross-section to a square cross-section, which illustratesthe formation of a tubular hydraulically settable article having ahollow square cross-section with filaments placed in a helical andparallel configuration around the longitudinal axis of the article;

FIG. 21 is a perspective view of an apparatus with a cut-away view of afilament placement chamber containing multiple mandrels, whichillustrates the formation of a hydraulically settable brick withfilaments placed in a parallel configuration along the length of thebrick;

FIG. 22 is a perspective view of an apparatus for placing filaments intoa hydraulically settable mixture while simultaneously extruding thehydraulically settable mixture;

FIG. 23 is a side elevational view of an apparatus for placing filamentsinto a hydraulically settable mixture while simultaneously extruding thehydraulically settable mixture;

FIG. 24 is a longitudinal cross-section view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture taken along cutting planeline 24--24 of FIG. 22;

FIG. 25 is an exploded perspective view of an apparatus for placingfilaments into a hydraulically settable mixture while simultaneouslyextruding the hydraulically settable mixture;

FIG. 26 is a perspective view of an apparatus forming a hydraulicallysettable pipe having filaments extending along the length of the pipe ina parallel configuration as placed by a set of fixed placing means in afixed channel carriage shown in a cut-away view with filaments beingdispensed from filament spools on a fixed feeder ring;

FIG. 27 is a perspective view of an apparatus forming a hydraulicallysettable pipe having filaments extending along the length of the pipe ina helical configuration as placed by a set of rotatable placing means ina rotatable channel carriage shown in a cut-away view with filamentsbeing dispensed from filament spools on a rotatable feeder ring;

FIG. 28 is a perspective view of an apparatus forming a hydraulicallysettable pipe having filaments extending along the length of the pipe ina criss-cross configuration as placed by two sets of rotatable placingmeans, one set is in a rotatable channel carriage shown in a cut-awayview with filaments being dispensed from filament spools on a rotatablefeeder ring;

FIG. 29 is a perspective view of an apparatus forming a hydraulicallysettable pipe having filaments extending along the length of the pipe ina parallel configuration and a criss-cross configuration as placed by afixed placing means and two sets of rotatable placing means, one set isin a rotatable channel carriage shown in a cut-away view with filamentsbeing dispensed from filament spools on a rotatable feeder ring;

FIG. 30 is a graph illustrating the relationship between the burststrength of a hydraulically settable article containing spiral woundfilaments which was produced using conventional methods and thepercentage of filaments within the article;

FIG. 31 is a graph illustrating the relationship between the burststrength of a hydraulically settable article containing spiral woundfilaments which was produced using conventional methods and the windingangle of the filaments within the article;

FIG. 32 is a graph illustrating the relationship between the modulus ofelasticity of a hydraulically settable article containing spiral woundfilaments which was produced using conventional methods and thepercentage of filaments within the article; and

FIG. 33 is a graph illustrating the relationship between the modulus ofelasticity of a hydraulically settable article containing spiral woundfilaments which was produced using conventional methods and the windingangle of the filaments within the article.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention encompasses novel compositions, methods, andapparatus for the continuous placement of filaments within and duringthe extrusion of hydraulically settable mixtures into a desired article.The continuous filaments increase the flexural, tensile, and hoopstrengths, as well as the toughness, flexibility, and elongation abilityof the hydraulically settable article. A variety of articles can beformed, including those which have thin walls, complicated shapes,and/or highly critical tolerances. In addition, relatively large,thick-walled objects such as "two-by-fours" or other structural objectscan also be efficiently extruded and impregnated with filaments usingthe compositions, methods, and apparatus of the present invention. Suchextruded articles are immediately (or in a manner of seconds)form-stable upon being extruded.

The novel hydraulically settable compositions can generally be describedas multi-component, multi-scale, fiber-reinforced, micro-composites. Bycarefully incorporating a variety of different materials (includinginorganics and fibers) capable of imparting discrete yet synergisticallyrelated properties, it is possible to create a unique class or range ofmicrocomposites having remarkable properties of strength, toughness,environmental soundness, mass-producibility, and low cost.

The term "multi-component" refers to the fact that the hydraulicallysettable materials of the present invention typically include three ormore chemically or physically distinct materials or phases, such asfibers, filaments, inorganic aggregate materials, organic aggregatematerials, hydraulically settable materials, organic theology-modifyingagents, dispersants, water, and other liquids. Each of these broadcategories of materials imparts one or more unique properties to thefinal article extruded therefrom (as well as the mixture used to formthe article). Within these broad categories it is possible to furtherinclude different components (such as two or more inorganic aggregatesor fibers) which can impart different, yet complementary, properties tothe extruded article. This allows for the specific engineering ofdesired properties within the article in conjunction the extrusionprocess.

The term "multi-scale" refers to the fact that the compositions andmaterials of the present invention are definable at different levels orscales. Specifically, within the hydraulically settable materials of thepresent invention there is typically a macro-component composition inthe range from about 0.01 mm to as high as about 10 mm, amicro-component composition in the range of about 10 nanometers to about10 microns, and a submicron component. Although these levels may not befractal, they are usually very similar to each other, and homogeneousand uniform within each level.

The term "fiber-reinforced" is self-explanatory, although it may alsofairly be applied to the reinforcing action of the filaments as well asfibers. The structural matrix of the hydraulically settable materials ofthe present invention relies on the bond or interaction between thehydraulically settable binder, inorganic aggregate, therheology-modifying agent, the fibers, and the filaments. The fibers andfilaments act primarily as reinforcing components to specifically addductility, tensile strength, flexural strength, hoop strength,flexibility, and elongation ability.

Finally, the term "micro-composite" refers to the fact that thehydraulically settable materials are not merely a compound or mixturebut a designed matrix of specific, discrete materials on a micro-level,which are of different sizes, shapes, and chemical make-up. Thematerials are sufficiently well bound and interactive so that the uniqueproperties of each are fully evidenced in the final composite (e.g., thetensile strength of the matrix has a direct correlation to the tensilestrengths of the fibrous and filament components; the burst or hoopstrength of a hollow article has a direct correlation to the filamentstrength, diameter, placement angle, and concentration; etc.).

In light of these definitions and principles, materials that include ahydraulically settable binder, an inorganic aggregate, water,(optionally) fibers (both organic and inorganic), and (optionally) anorganic rheology-modifying agent can be combined and extruded into avariety of articles. Such articles can have a variety of differentstrength, toughness, and density characteristics, and can have highlycritical tolerances. This allows the hydraulically settable materials ofthe present invention to be continuously extruded and filament wound(and, hence, mass produced) into a variety of articles presently madefrom, e.g., plastic, metal, wood, or clay.

As described more fully hereinafter, the basic parameters of thehydraulically settable mixtures of the present invention include (1) theparticle packing density, (2) the amount of hydraulically settablebinder (usually hydraulic cement), (3) the amount of water, (4) theextrusion pressure, (5) the rheology (including the yield stress andgreen strength), and (6) the strength of the final cured product(including compressive and tensile strengths).

I. GENERAL DISCUSSION.

A. General Description of the Extrusion Process.

Hydraulically settable products, including cementitious materials andthe methods of utilizing them, have been known for millennia. The typesof cementitious or other hydraulically settable products that have beenmade are various and numerous, although they share the common quality ofgenerally being large and bulky. In particular, cementitious objectsgenerally require significant size and mass in order to achieve thedesired strength and other performance criteria. Typical cementitiousmaterials also require relatively extensive setting and curing timesbefore they can be demolded. The moldability and/or extrudability ofmost hydraulically settable mixtures is generally limited by thetradeoff between workability and form-stability. Increasing one usuallydecreases the other, leaving only a narrow range of acceptablerheologies.

The present invention overcomes this tradeoff between extrudability andform-stability by creating a highly plastic and cohesive hydraulicallysettable mixture that is form-stable immediately or shortly after beingextruded. The term "plastic" refers to a hydraulically settable mixturethat is workable, which will flow under pressure, and which hassufficient cohesive strength so as to be form-stable in the green state(green strength or form-stability is either immediate or within a matterof seconds).

The unique properties of the hydraulically settable mixtures madeaccording to the present invention result from carefully controlledrheology, preferably by optimizing the particle packing density, asdescribed more fully below, coupled with a deficiency of water. Thedeficiency of water yields a relatively stiff, or highly viscous,hydraulically settable mixture because there is insufficient water tocompletely fill the interstices between the particles, leavinginsufficient water to fully lubricate the particles. In cases wherethere is very low initial water, the hydraulically settable mixture mayconsist of dry-looking granulates that lack cohesion and do not holdtogether as a single mass.

However, by exposing the water deficient mixture to increased mechanicalpressure by an auger or piston extruder, as well as by applying a vacuumto the mixture in order to substantially evacuate the air within theinterstitial space, the particles within the hydraulically settablemixture compress together, thereby increasing their packing density.This in turn reduces the effective water deficiency, thus allowing thewater to more completely fill the interstices between the more denselypacked particles. The apparent increase in the water that is availableto fill the interstices better lubricates the particles, reduces theinterparticulate friction, and allows the mixture to flow more easily bytemporarily decreasing the yield stress. In addition, vibrating themixture may also decrease the viscosity of a water deficient mixture.

Upon exiting the die, the reduction in pressure exerted on thehydraulically settable mixture allows the material to expand slightlyand return to a slightly less optimized state of particle packing. Thisin turn creates a partial vacuum or negative pressure within thecapillaries and strong meniscus forces are created that hold thehydraulically settable material together. The sudden lack of pressure(and lower shear rate) increases the viscosity of the material which,together with a high yield stress at the zero sheer rate, reduces theamount of water available to lubricate the particles, and results in animmediate increase in form-stability.

The rheology of the hydraulically settable mixture may also beinfluenced by other additives within the cementitious mixture, such ascellulose-, starch-, or protein-based or synthetic organicrheology-modifying agents, which increase the yield stress of themixture while not significantly increasing or decreasing the viscosityto the point of unworkability. Under the high shear conditions withineither an auger or piston extruder, the higher yield stress is overcome,the plastic viscosity is temporarily lowered, and the mixture has atemporary increase in its ability to flow. Once the hydraulicallysettable material has been extruded and the shear forces have beenremoved, the rheology-modifying agent aids in creating a more cohesive,form-stable extruded product. Hence, the rheology-modifying agent helpsto create a hydraulically settable mixture that exhibits sheer thinning,thixotropic, or pseudo-plastic behavior, that is, a material which hasan apparent decrease in viscosity when subjected to shear forces,including pressure and vibration.

In addition to imparting desired rheological properties to the mixture,optimizing the particle packing within the mixture greatly increases thefinal strength of the cured product by reducing the amount of water andair within the hydraulically settable matrix. According to the StrengthEquation below, the compressive strength of a cured cementitious producthas been found to be inversely proportional to the amount of added waterand interstitial air (σ is the comprehensive strength of the curedcementitious product; k represents the highest possible theoreticalstrength, assuming no interstitial water or air, and is usually about300-500 MPa, although it may be as high as 800 MPa in some cases, suchas where the extruded article is cured by autoclaving; V_(c) is thevolume of cement; V_(w) is the volume of water; and V_(a) is the volumeof air or interstitial space within a cementitious mixture):

    σ=k[V.sub.c /(V.sub.c +V.sub.w +V.sub.a)].sup.2 MPa

In normal, uncompacted cement paste, k=340 MPa, while in a highlycompacted system k=500 MPa. The size of k therefore depends on theprocessing technique, but is constant for the same technique. Ingeneral, reducing the amount of air and water within the hydraulicallysettable mixture will both increase the strength of the final curedmaterial. Both can be reduced while also improving the workability ofthe hydraulically settable mixture by increasing the particle packingdensity, as set forth more fully below. In addition, increasing theextrusion pressure and attendant compaction during the extrusion processcan also greatly reduce the amount of interstitial air, whilemaintaining adequate flowability where a higher water deficiency (lesswater) is used.

In cases where the particle packing density of the hydraulicallysettable mixture has been optimized to the higher end of the rangesdiscussed herein, a relatively high extrusion pressure capable ofeliminating most of the interstitial air is used, and very little wateris added initially, articles of manufacture having a hydraulicallysettable matrix can be extruded which have compressive strengths higherthan 500 MPa, even approaching 800 MPa if autoclaved, for example.

It is true that high strength concrete products have been made in alaboratory setting which have low water and low interstitial air.However, they are generally formed by isostatic compaction (often drypacked) under extreme pressures, usually by means of high pressuremolding greater than about 70 MPa. However, these methods are notadaptable to the economical mass production of cementitious materials,nor do they allow for the molding of anything but the simplest, mostrudimentary forms. They certainly do not allow for the continuousformation by extrusion of large volumes of form-stable hydraulicallysettable articles such as are possible using the compositions andmethods of the present invention. Moreover, extrusion provides a morecontinuous method for mass producing certain articles, such as thosethat are relatively long and narrow and have a constant cross-sectionalshape and dimension, compared to conventional molding processes.

Besides incorporating into the hydraulically settable matrix filaments,as discussed more fully below, it may also be desirable to co-extrudethe hydraulically settable mixture with other materials in order toobtain, e.g., a laminate structure or an extruded product with othermaterials impregnated within or extruded over the surface of thehydraulically settable matrix. Things which may be co-extruded with theextrudable hydraulically settable mixtures of the present inventioninclude another hydraulically settable mixture (often having differentor complementary properties), a fibrous mat, graphite (to form pencils),coating materials, polymers, clays, and continuous strips, wires, orsheets of almost any other material (such as metal). It has been foundthat by joining together, for example, a hydraulically settable sheetand a fibrous mat by co-extrusion, the final product exhibitssynergistic results of strength, toughness, and other desirableproperties.

After the hydraulically settable mixture has been extruded into thedesired shape, it may be allowed to harden in the extruded shape. Thehardening process may be accelerated by heating the object, such as bymeans of heating under controlled high relative humidity or highpressure autoclaving. Alternatively, the extruded shape may further bealtered or manipulated, such as by passing an extruded sheet between apair of rollers in order to reduce the thickness of the sheet and/orimprove the surface quality of the sheet. The extruded object may alsobe curved, bent, cut, or further molded using any known molding processinto a wide variety of other objects or shapes.

B. Extruded Shapes and Articles.

Terms such as "extruded shape", "extruded article" and "hydraulicallysettable article", as used in this specification and the appendedclaims, are intended to include any known or future designed shape orarticle formed by continuously extruding, and impregnating withfilaments, the hydraulically settable compositions of the presentinvention. An illustrative, yet by no means exhaustive, list of theextruded shapes or articles which may be manufactured according to thepresent invention includes rectangular, square, elliptical, orcylindrical rods or bars, concrete rebars, pipes, tubes, straws,cylinders, multicellular structures, boards, I-beams, "two-by-fours",window frames, bricks, roofing tiles, and pencils.

In addition, the terms "extruded article", "extruded shape" and"hydraulically settable article" are also intended to include allprecursor shapes or articles that are initially formed by extruding thecompositions of the present invention, impregnating the extruded articlewith filaments, but which are thereafter manipulated, augmented, orotherwise formed into other shapes or articles. For example, an extrudedbar or pipe which is initially straight might be curved into a curvedbar. Both straight and curved bars or pipes are within the purview ofthe present invention and are intended to fall within the definition ofan "extruded article", "extruded shape" or "hydraulically settablearticle".

These terms are also intended to include any extruded article or shapewhich is intended to be incorporated into any other article, whether ornot such article is also within the scope of this patent. While thecombination of extruded articles, or the combination of an extrudedarticle and any other article, might have independently patentablefeatures, the subpart obtained using the methods and apparatus of thepresent invention is intended to fall within the terms "extrudedobject", "extruded article" or "hydraulically settable article", aswould any combination of subparts.

C. Microstructural Engineering Design.

As mentioned above, the hydraulically settable compositions of thepresent invention have been developed from the perspective of a microstructural engineering and materials science approach in order to buildinto the microstructure of the hydraulically settable matrix certaindesired, predetermined properties, while at the same time remainingcognizant of costs and other manufacturing complications. Furthermore,this microstructural engineering analysis approach, in contrast to thetraditional trial-and-error, mix-and-test approach, has resulted in theability to design hydraulically settable materials with those propertiesof strength, weight, insulation, cost, and environmental neutrality thatare necessary in order to extrude a wide variety of hydraulicallysettable objects in a significantly more efficient manner thanpreviously possible.

The number of different raw materials available to engineer a specificproduct is enormous, with estimates ranging from between fifty thousandand eighty thousand. They can be drawn from such disparately broadclasses as metals, polymers, elastomers, ceramics, glasses, composites,and cements. Within a given class, there is some commonality inproperties, processing, and use-patterns. Ceramics, for instance, have ahigh modulus of elasticity, while polymers have a low modulus; metalscan be shaped by casting and forging, while composites require lay-up orspecial molding techniques; hydraulically settable materials, includingthose made from hydraulic cements historically have low flexuralstrength, while elastomers have high flexural strength.

However, compartmentalization of material properties has its dangers; itcan lead to specialization (the metallurgist who knows nothing ofceramics) and to conservative thinking ("we use steel because that iswhat we have always used"). In part, it is this specialization andconservative thinking that has limited the consideration of usinghydraulically settable materials for a variety of products such asextruded shapes, particularly those with relatively thin walls,complicated shape or highly critical tolerances.

Nevertheless, once it is realized that hydraulically settable materialshave such a wide utility and can be microstructurally designed andengineered, then their applicability to a variety of possible productsbecomes obvious. Hydraulically settable materials have an additionaladvantage over other conventional materials in that they gain theirproperties under relatively gentle and nondamaging conditions. (Othermaterials require high energy, severe heat, or harsh chemical processingthat significantly affects the material components.) Therefore, manynonhydraulically settable materials, including filaments, can beincorporated into hydraulically settable materials without damage andwith surprising synergistic properties or results if properly designedand engineered.

The design of the compositions of the present invention has beendeveloped and narrowed, first by primary constraints dictated by thedesign, and then by seeking the subset of materials which maximizes theperformance of the components. At all times during the process, however,it is important to realize the necessity of designing products which canbe manufactured in a cost-competitive process.

Primary constraints in materials selection are imposed bycharacteristics of the design of a component which are critical to asuccessful product. With respect to an extruded article, those primaryconstraints include desired weight and desired strength (e.g.,compressive, tensile, flexural, and hoop strength), toughness, and otherperformance criteria requirements, while simultaneously keeping thecosts comparable to their, e.g., plastic, wood, clay, or metalcounterparts.

As discussed above, one of the problems with hydraulically settablematerials in the past has been that they are typically poured into aform, worked, and then allowed to set, harden, and cure over a longperiod of time--even days or weeks. Experts generally agree that ittakes at least one month for traditional concrete products to reachtheir maximum strength. Even with expensive "set accelerators," thisstrength gain occurs over a period of days. Such time periods areusually impractical for the economic mass production of thehydraulically settable articles contemplated by the present invention.

As a result, an important feature of the present invention is that whenthe hydraulically settable mixture is extruded into the desired shape orarticle, it will maintain its shape (i.e., support its own weightsubject to minor forces, such as gravity and movement through theprocessing equipment) in the green state without external support.Further, from a manufacturing perspective, in order for production to beeconomical, it is important that the extruded object rapidly (in amatter of seconds) achieve sufficient strength so that it can be handledusing ordinary manufacturing procedures, even though the hydraulicallysettable mixture may still be in a green state and not fully hardened.

Another advantage of the microstructural engineering and materialsscience approach of the present invention is the ability to developcompositions in which cross-sections of the structural matrix are morehomogeneous than have been typically achieved in the prior art. Ideally,when any two given samples of about 1-2 mm³ of the hydraulicallysettable matrix are taken, they will have substantially similar amountsof hydraulically settable binder particles, hydraulically settablebinder gel, aggregates, fibers, filaments, rheology-modifying agents,and any other additives.

In its simplest form, the process of using a materials science analysisin microstructurally engineering and designing a hydraulically settablematerial comprises characterizing, analyzing, and modifying (ifnecessary): (a) the aggregates, (b) the particle packing, (c) the systemrheology, and (d) the processing and energy of the manufacturing system.In characterizing the aggregates, the average particle size isdetermined, the natural packing density of the particles (which is afunction of the actual particle sizes and morphology) is determined, andthe strength of the particles is ascertained. (Unreacted or previouslyreacted hydraulically settable binder particles may be considered to bean aggregate.)

With this information, the particle packing can be predicted accordingto mathematical models. It has been established that the particlepacking is a primary factor for designing desired requirements of theultimate product, such as workability, form-stability, shrinkage, bulkdensity, insulative capabilities, tensile, compressive, and flexuralstrengths, elasticity, durability, and cost optimization. The particlepacking is affected not only by the particle and aggregatecharacterization, but also by the amount of water and its relationshipto the interstitial void volume of the packed aggregates.

System rheology is a function of both macro-rheology and micro-rheology.The macro-rheology is the relationship of the solid particles withrespect to each other as defined by the particle packing. Themicro-rheology is a function of the lubricant fraction of the system. Bymodification of the lubricants (which may be water, rheology-modifyingagents, plasticizers, dispersants, other materials, or a combination ofthese), the viscosity and yield stress can be modified. Themicro-rheology can also be modified physically by changing the shape andsize of the particles, e.g., the use of chopped fibers, plate-like mica,round-shaped silica fume, rhombic fused silica, or crushed, angular, orgranular hydrated binder particles, each of which will interact with thelubricants differently.

Finally, the manufacturing processing can be modified to manipulate thebalance between workability and form-stability. In general, lowering theviscosity of the mixture increases the workability, while increasing theyield stress increases the form-stability of the extruded material. Asapplied to the present invention, it is generally optimal to maintain aminimum desired yield stress while minimizing the viscosity. Molding ordeformation of the material only occurs when a force greater than theyield stress of the hydraulically settable mixture is applied.

The yield stress and, hence, the form-stability of the extruded objectcan also be increased by either chemical additives (such as by adding arheology-modifying agent) or by adding energy to the system (such as byheating the extrusion apparatus or the extruded materials). For example,heating the material as it is extruded can activate a starch additive,thereby causing it to increase the yield stress of the extrudedmaterial. In addition, heat accelerates the hydration reaction betweenthe hydraulically settable binder and water, sometimes by factors ashigh as 10 or even 20 times the normal reaction rate. Indeed, it is thisdiscovery of how to manipulate the hydraulically settable compositionsin order to increase the form-stability of the compositions whileobtaining good flow during the formation process that make the presentinvention such a significant advancement in the art.

From the following discussion, it will be appreciated how each of thecomponent materials within the hydraulically settable mixture, as wellas the processing parameters, contributes to the primary designconstraints of the extrudable hydraulically settable mixtures so that awide variety of extruded articles can be produced therefrom. Specificcompositions are set forth in the examples given later in order todemonstrate how the maximization of the performance of each componentaccomplishes the combination of desired properties.

D. Hydraulically Settable Materials.

The materials used to manufacture the extruded articles of the presentinvention develop strength through the chemical reaction of water and ahydraulically settable binder, such as hydraulic cement, calcium sulfate(or gypsum) hemihydrate (which is sometimes mixed with gypsum anhydride,commonly known as "anhydrite"), and other substances which harden afterbeing exposed to water. Even slag, blast furnace slag, fly ash, orsilica fume may be activated and act as a "hydraulically settablebinder."

The term "hydraulically settable materials" as used in thisspecification and the appended claims includes any material with astructural matrix and strength properties that are derived from ahardening or curing of a hydraulically settable binder. These includecementitious materials, plasters, and other hydraulically settablematerials as defined herein. The hydraulically settable binders used inthe present invention are to be distinguished from other cements orbinders such as polymerizable, water insoluble organic cements, glues,or adhesives.

The terms "hydraulically settable material," "hydraulic cementmaterials," or "cementitious materials," as used herein, are intended tobroadly define compositions and materials that contain both ahydraulically settable binder and water, regardless of the extent ofhydration or curing that has taken place. Hence, it is intended that theterm "hydraulically settable materials" shall include hydraulic paste orhydraulically settable mixtures in a green (i.e., unhardened) state, aswell as hardened hydraulically settable or concrete products. While in agreen state, hydraulically settable materials may also be referred to as"hydraulically settable mixtures."

1. Hydraulically Settable Binders.

The terms "hydraulically settable binder" or "hydraulic binder," as usedin this specification and the appended claims, are intended to includeany inorganic binder (such as hydraulic cement, gypsum hemihydrate,calcium oxide, or mixtures thereof) which develops strength propertiesand hardness by chemically reacting with water and, in some cases, withcarbon dioxide in the air and water. The terms "hydraulic cement" or"cement" as used in this specification and the appended claims areintended to include cement clinker and crushed, ground, milled, andprocessed clinker in various stages of pulverization and in variousparticle sizes.

Examples of typical hydraulic cements known in the art include the broadfamily of portland cements (including ordinary portland cement withoutgypsum), MDF cement, DSP cement, Densit-type cements, Pyrament-typecements, calcium aluminate cements (including calcium aluminate cementswithout set regulators), plasters, silicate cements (includingβ-dicalcium silicates, tricalcium silicates, and mixtures thereof),gypsum cements, phosphate cements, high alumina cements, micro finecements, slag cements, magnesium oxychloride cements, and aggregatescoated with microfine cement particles. The term "hydraulic cement" isalso intended to include other cements known in the art, such asα-dicalcium silicate, which can be made hydraulic under hydratingconditions within the scope of the present invention.

The basic chemical components of, e.g., portland cement include CaO,MgO, SiO₂, Al₂ O₃, Fe₂ O₃, SO₃, in various combinations and proportions.These react together in the presence of water in a series of complexreactions to form insoluble calcium silicate hydrates, carbonates (fromCO₂ in the air and added water), sulfates, and other salts or productsof calcium, magnesium, aluminum, and iron, together with hydratesthereof. These include tricalcium aluminate, dicalcium silicate,tricalcium silicate, and tetracalcium alumina ferrite. The aluminum andiron constituents are thought to be incorporated into elaboratecomplexes within the aforementioned materials. The cured cement productis a complex matrix of insoluble hydrates and salts which are complexedand linked together much like stone. This material is highly inert andhas both physical and chemical properties similar to those of naturalstone or dirt.

Gypsum is also a hydraulically settable binder that can be hydrated toform a hardened binding agent. One hydratable form of gypsum is calciumsulfate hemihydrate, commonly known as "gypsum hemihydrate." Thehydrated form of gypsum is calcium sulfate dihydrate, commonly known as"gypsum dihydrate." Calcium sulfate hemihydrate can also be mixed withcalcium sulfate anhydride, commonly known as "gypsum anhydrite" orsimply "anhydrite."

Although gypsum binders or other hydraulically settable binders such ascalcium oxide are generally not as strong as hydraulic cement, highstrength may not be as important as other characteristics (e.g., therate of hardening) in some applications. In terms of cost, gypsum andcalcium oxide have an advantage over hydraulic cement because they aresomewhat less expensive.

In addition, gypsum hemihydrate is known to set up or harden in a muchshorter time period than traditional cements. In fact, in use with thepresent invention, it will harden and attain most of its ultimatestrength within about thirty minutes. Hence, gypsum hemihydrate can beused alone or in combination with other hydraulically settable materialswithin the scope of the present invention. It has been found that addinggypsum hemihydrate to a hydraulically settable mixture containinghydraulic cement as a binder yields a mixture having a much lowerwater-to-cement ratio and, hence, higher strength according to theStrength Equation.

Terms such as "hydrated" or "cured" hydraulically settable mixture,material, or matrix refers to a level of substantial water-catalyzedreaction which is sufficient to produce a hydraulically settable producthaving a substantial amount of its potential or final maximum strength.Nevertheless, hydraulically settable materials may continue to hydratelong after they have attained significant hardness and a substantialamount of their final maximum strength.

Terms such as "green" or "green state" are used in conjunction withhydraulically settable mixtures which have not achieved a substantialamount of their final strength, regardless of whether such strength isderived from artificial drying, curing, or other means. Hydraulicallysettable mixtures are said to be "green" or in a "green state" justprior and subsequent to being molded into the desired shape. The momentwhen a hydraulically settable mixture is no longer "green" or in a"green state" is not necessarily a clear-cut line of demarcation, sincesuch mixtures generally attain a substantial amount of their totalstrength only gradually over time. Hydraulically settable mixtures can,of course, show an increase in "green strength" and yet still be"green." For this reason, the discussion herein often refers to theform-stability of the hydraulically settable material in the greenstate.

As mentioned above, preferred hydraulically settable binders includeportland white cement, portland grey cement, micro fine cement, highalumina cement, slag cement, gypsum hemihydrate, and calcium oxide,mainly because of their low cost and suitability for the manufacturingprocesses of the present invention. This list of cements is by no meansexhaustive, nor in any way is it intended to limit the types of binderswhich would be useful in making the hydraulically settable containerswithin the scope of the claims appended hereto. It has been found thatportland grey cement improves the cohesive nature of the greenhydraulically settable mixture better than other types of cements.

Additional types of hydraulic cement compositions include those whereincarbon dioxide is mixed with hydraulic cement and water. Hydrauliccement compositions made by this method are known for their ability tomore rapidly achieve high green strength. This type of hydraulic cementcomposition is discussed in U.S. Pat. No. 5,232,496 issued Aug. 3, 1993to Hamlin M. Jennings, Ph.D., and Simon K. Hodson, wherein water andhydraulic cement are mixed in the presence of a carbonate sourceselected from the group consisting of carbon dioxide, carbon monoxide,carbonate salts, and mixtures thereof. For purposes of disclosure, theforgoing patent is incorporated herein by specific reference.

2. Hydraulic Paste.

In each embodiment of the present invention, the hydraulic paste(including cement paste) is the key constituent which eventually givesthe extruded object the ability to set up and develop strengthproperties. The term "hydraulic paste" shall refer to a hydraulicallysettable binder which has been mixed with water. More specifically, theterm "cement paste" shall refer to hydraulic cement which has been mixedwith water. The terms "hydraulically settable," "hydraulic," or"cementitious" mixture shall refer to a hydraulic cement paste to whichaggregates, fibers, rheology-modifying agents, dispersants, or othermaterials have been added, whether in the green state or after it hashardened and/or cured. The other ingredients added to the hydraulicpaste serve the purpose of altering the properties of the unhardened, aswell as the final hardened product, including, but not limited to,tensile strength, compressive strength, shrinkage, flexibility, bulkdensity, color, porosity, surface finish, and texture.

Although the hydraulically settable binder is understood to be thecomponent which allows the hydraulically settable mixture to set up, toharden, and to achieve much of the strength properties of the material,certain hydraulically settable binders also aid in the development ofbetter early cohesion and green strength. For example, hydraulic cementparticles are known to undergo early gelating reactions with water evenbefore it becomes hard; this can contribute to the internal cohesion ofthe mixture.

It is believed that aluminates, such as those more prevalent in portlandgrey cement (in the form of tricalcium aluminates and tetracalciumalumina ferrites) are responsible for a colloidal interaction betweenthe cement particles during the earlier stages of hydration. This inturn causes a level of flocculation/gelation to occur between the cementparticles. The gelating, colloidal, and flocculating effects of suchbinders has been shown to increase the moldability (i.e., plasticity) ofhydraulically settable mixtures made therefrom.

The percentage of hydraulically settable binder within the overallmixture varies depending on the identity of the other addedconstituents. However, the hydraulically settable binder is preferablyadded in an amount ranging from between about 1% to about 90% as apercentage by weight of the wet hydraulically settable mixture, morepreferably within the range from between about 8% to about 60%, and mostpreferably from about 10% to about 45%. From the disclosure and examplesset forth herein, it will be understood that this wide range of weightpercentages covers the many different types of articles that may beformed by extruding a hydraulically settable mixture.

Despite the foregoing, it will be appreciated that all concentrationsand amounts are critically dependent upon the qualities andcharacteristics that are desired in the final product. For example, in avery thin-walled structure (even as thin as 0.05 mm) where high strengthis needed, it may be more economical to have a very high percentage ofhydraulically settable binder with little or no aggregate. In such acase, it may be desirable to include a high amount of fiber to impartflexibility and toughness.

The other important constituent of hydraulic paste is water. Bydefinition, water is an essential component of the hydraulicallysettable materials within the scope of the present invention. Thehydration reaction between hydraulically settable binder and wateryields reaction products which give the hydraulically settable materialsthe ability to set up and develop strength properties.

In most applications of the present invention, it is important that thewater to hydraulically settable binder ratio be carefully controlled inorder to obtain a hydraulically settable mixture which after extrusionis self-supporting in the green state. Nevertheless, the amount of waterto be used is dependent upon a variety of factors, including the typesand amounts of hydraulically settable binder, aggregates, fibrousmaterials, rheology-modifying agents, and other materials or additiveswithin the hydraulically settable mixture, as well as the extrusionconditions to be used, the specific article to be extruded, and itsproperties.

The preferred amount of added water within any given application isprimarily dependent upon two key variables: (1) the amount of waterwhich is required to react with and hydrate the binder; and (2) theamount of water required to give the hydraulically settable mixture thenecessary rheological properties and workability.

In order for the green hydraulically settable mixture to have adequateworkability, water must generally be included in quantities sufficientto wet each of the particular components and also to at least partiallyfill the interstices or voids between the particles (including, e.g.,binder particles, aggregates, and fibrous materials). If water solubleadditives are included, enough water must be added to dissolve orotherwise react with the additive. In some cases, such as where adispersant is added, workability can be increased while using lesswater.

The amount of water must be carefully balanced so that the hydraulicallysettable mixture is sufficiently workable, while at the same timerecognizing that lowering the water content increases both the greenstrength and the final strength of the hardened, extruded product. Theappropriate rheology to meet these needs can be defined in terms ofyield stress. In order for the hydraulically settable mixtures to haveadequate green strength and form-stability upon being extruded into thedesired article, the hydraulically settable mixture will preferably havea yield stress greater than or equal to about 2 kPa, more preferablygreater than or equal to about 10 kPa, and most preferably greater thanor equal to about 100 kPa. It should be understood that these figuresrepresent preferred minima. There is no limit to the yield stress which,depending on a number of factors, such as the water deficiency, themorphology of the particles or, the amount of rheology-modifying agentwithin the mixture, may be much higher. The desired level of yieldstress can be (and may necessarily have to be) adjusted depending on theparticular shape or article to be extruded.

Because the hydraulically settable mixtures of the present inventionexhibit shear thinning, there is no single preferred viscosity, althoughthe mixtures should have a viscosity adequate to make them form-stablebut small enough to render them flowable using an extruder. In general,however, the apparent viscosity will usually be about 10⁷ poise orgreater at a shear rate of 0 s⁻¹, about 10⁴ poise or greater at a shearrate of 20 s⁻¹, and about 2×10² poise or greater at a shear rate of 1000s⁻¹.

One skilled in the art will understand that when more aggregates orother water absorbing additives are included, a higher water tohydraulically settable binder ratio is necessary in order to provide thesame level of workability and available water to hydrate thehydraulically settable binder. This is because a greater aggregateconcentration provides a greater volume of interparticulate intersticesor voids which must be filled by the water as a fraction of thehydraulically settable binder volume. Porous aggregates can alsointernally absorb significant amounts of water due to their high voidcontent. Based on the foregoing qualifications, typically hydraulicallysettable mixtures within the scope of the present invention will have awater to hydraulically settable binder ratio within a range from about0.05 to about 4, preferably about 0.1 to about 1, and most preferablyfrom about 0.15 to about 0.5.

Because of the higher levels of particle packing density of thehydraulically settable binder particles within a typical mixture of thepresent invention, the specific gravity of the hydraulic paste fractionof the hydraulically settable mixture will preferably (in cases wherehigher strength is desired) be greater than about 2.2, more preferablygreater than about 2.5, and most preferably greater than about 2.6.

It should be understood that the hydraulically settable binder has aninternal drying effect on the hydraulically settable mixture because thebinder particles chemically react with water and reduce the amount offree water within the interparticulate interstices. This internal dryingeffect can be enhanced by including faster reacting hydraulicallysettable binders, such as gypsum hemihydrate, along with slower reactinghydraulic cement.

3. Water Deficiency.

In many cases, the amount of water needed to both hydrate the binder andalso impart the desired rheology to the hydraulically settable mixturemay be more accurately described in terms of either volume percent or"water deficiency." The level of water deficiency is determined bysubtracting the volume of free interstitial water from the totalinterstitial space, and then dividing the result by the totalinterstitial space.

    water deficiency=(V.sub.space -V.sub.water)/V.sub.space

By way of example, and in order to better illustrate the concept ofwater deficiency, the hydraulically settable mixture can contain addedwater and yet be 100% water deficient (i.e., have no interstitial water)in the case where all of the water has either been absorbed into thepores of the aggregates or reacted with the hydraulically settablebinder.

Of course, it should be understood that the amount of water that hasactually reacted with the hydraulically settable binder at any giventime after the hydraulically settable binder and water have been mixedtogether will usually be significantly lower than the calculatedstoichiometric equivalent of water needed to substantially hydrate thebinder. Because of the kinetics of the hydration reaction, the waterdoes not immediately react completely with the hydraulically settablebinder, but only over time and generally during the curing stage afterthe material has been extruded.

Hence, water within the theoretical stoichiometric equivalent amountwhich does not react with the binder is generally available to fill theinterstices or voids between the particles (if not absorbed by theaggregate material). Water that has not chemically reacted with thehydraulically settable binder may be classified as either gel water orcapillary water. Both forms tend to decrease the strength of the finalcured material and, hence, should be minimized where possible. Becausethe amount of water available to fill the interstices directly affectsthe workability and rheology of the hydraulically settable mixture, itwill usually be necessary to determine the amount of unboundstoichiometric water available to fill the interstices and lubricate theparticles at any given time after mixing, although initially almost allof the added water is free because of the slowness of the hydrationreaction.

Some of the factors that will determine what percentage of thecalculated stoichiometric equivalent of water will have actually reactedwith the hydraulically settable binder, include the reactivity (or rateof reaction) of the binder, the temperature of the mixture, the particlesize of the binder, the level of mixing, the wettability of thecomponents within the overall mixture, and the time which has elapsedsince the addition of water.

For example, hydraulically settable binders having a high rate ofreaction will absorb or react with the available water more quickly thanbinders having lower rates of reaction. As with most reactions, highertemperatures generally will increase the rate of reaction of allhydraulically settable binders, and hence, the rate of water removal ofthe binder.

Moreover, hydraulically settable binders with smaller particle sizeswill also tend to react with more water because they will have a greateroverall surface area that will come in contact and react with theavailable water. Of course, the tendency of the hydraulically settablebinder particles to react with water is dependent upon the level ofmixing. More thoroughly blended mixtures will result in greater contactbetween water and binder particles, and, hence, greater reaction withthe water.

The extent of any reaction that has not reached equilibrium is alsodependent upon the time which has elapsed since the reactants have beenmixed together. Obviously, a hydraulically settable mixture in which thehydraulically settable binder has been in contact with water over agreater period of time will show a greater level of reaction between thewater and the binder. Nevertheless, where a dispersant has been added,longer mixing time increases the specific surface area for adsorption ofthe dispersant, thereby creating a more fluid mixture in the short run.In general, substantial setting of hydraulic cement usually occurswithin about 5 hours.

Aside from the dynamics of the reaction between the hydraulicallysettable binder and water, the other components within the hydraulicallysettable mixture will also affect to some degree the absorption by orreaction of the water with the binder particles. Certain additives, suchas water soluble rheology-modifying agents, will compete with the binderparticles and actually absorb some of the available water.

In addition, other additives, such as dispersants, can impede thereaction between water and hydraulically settable binder particles.Whether a given component or reaction condition will increase ordecrease the reaction between the water and the hydraulically settablebinder particles must be carefully determined while designing anyparticular mix design. However, one skilled in the art will be able topredict the effect of a given component or reaction condition on thetendency of the water to react with the hydraulically settable binder,at least on the basis of empirical observation.

Once it has been determined how much water will actually react with thecement, the next step is to determine how much "interstitial water"should be added in addition to this reacted or absorbed amount.Interstitial water is the water which is available to fill the voids orinterstices and which will directly affect the workability of thehydraulically settable mixture. The preferred amount of interstitialwater that will be required is determined by a combination of factors,including the particle packing density of the mixture, thecompressibility of the mixture, and the pressure exerted on the mixtureby the extruder.

Knowing the particle packing density allows one to determine the volumeof interstitial space within the uncompressed mixture which willinitially be filled by interstitial water. Knowing the compressibilityof the mixture and the pressure that will be exerted allows one todetermine the expected reduction of interstitial space when thehydraulically settable mixture is subjected to a given pressure duringthe extrusion process.

Where the particle packing density is lower, there will be moreinterstitial space as a percentage of the overall volume of the mixture,and more water will be required to fill this space. Conversely, wherethe particle packing density is greater, there will be less interstitialspace as a percentage of the overall volume of the mixture, and lesswater will be required to fill this space. How to optimize the packingdensity will be discussed hereinafter.

Similarly, where the hydraulically settable mixture will be subjected toa greater amount of pressure during the extrusion process, thecompression step will more dramatically reduce the volume ofinterstitial space, which in turn means that less interstitial waterwill be required initially in order to achieve the desired rheology.Also, including less water (higher deficiency) allows the particles tobe brought into more intimate contact during the compression process,resulting in a final cured product having less porosity, higher density,and greater strength.

Conversely, where the hydraulically settable mixture will be subjectedto a lesser amount of pressure during the extrusion process, thecompression step will less dramatically reduce the volume ofinterstitial space, which in turn means that more interstitial waterwill be required initially in order to achieve the desired rheology.Certain aggregates, such as sand, have relatively low compressibility.(How much pressure that may be exerted on the hydraulically settablemixture without destroying the integrity of the aggregate particlestherein depends on the compressive strength of the aggregate particles.)

The key is to add just enough water in order to substantially occupy theinterstitial space when the mixture is compressed during the extrusionprocess. Adding more water than what is required to fill the intersticesduring the compression of the extruded mixture would reduce both thegreen strength of the extruded product as well as the final strength ofthe cured material (according to the Strength Equation).

In light of the foregoing, it has been found that adequate workabilityof a hydraulically settable mixture that will be subjected to increasedpressure can be obtained when a deficiency of water is included. Theamount of water may be expressed in terms of volume percent, and, ifdeficient, will be less than the volume of the interstitial space, whichis determined by subtracting the natural packing density from 1. Forexample, if the natural packing density is 65%, the mixture will bedeficient in water if the water is included in an amount of less thanabout 35% by volume of the mixture. The amount of water that is requiredto create adequate workability will depend somewhat on the relativequantities of the mixture components, such as the hydraulically settablebinder particles, aggregates, and fibers. Nevertheless, it is generallynot the identity or relative quantities of the components but theoverall volume and packing density of the components that will determinehow much water should be added to achieve a hydraulically settablemixture having the desired rheological and plastic-like properties.

The amount of added water may, therefore, be expressed in terms of"water deficiency" before the mixture is compressed during the extrusionprocess. In mixtures relying upon the principles of particle packing andwater deficiency in order to attain the desired rheology, the level ofwater deficiency will be within the broad range from between about 1% toabout 90%. Because the preferred level of water deficiency is highlydependent upon many other variables, such as the components of thehydraulically settable mixture, the rheology of the mixture, and thelevel of particle packing efficiency, as well as the desired propertiesof the extruded product, there is no more narrow preferred range ofwater deficiency. Where a high level of rheology-modifying agent isemployed, it may be possible to extrude a mixture having excess water(or "negative" water deficiency).

Nevertheless, for any given mixture it will usually be preferable toinclude the minimum quantity of water necessary to allow it to flowunder the desired extrusion pressure and have enough internal cohesionto hold together once an article has been extruded from the mixture. Theminimum amount of water necessary for the hydraulically settable mixtureto flow may further be reduced by the addition of admixtures, such asplasticizers or dispersants, as set forth more fully herein. Where verylow levels of water are employed, it may be necessary in some cases topelletize the hydraulically settable mixture in order to increase theextrudability of the mixture.

Nevertheless, as a general rule, a mixture having a greater waterdeficiency will generally be stiffer and have lower workabilityinitially. Conversely, a mixture having a lower water deficiency willgenerally have lower viscosity and greater workability initially. Thelevel of stiffness, viscosity, or workability that will be desired forany given mixture will depend upon the extrusion process of a givensituation. Of course, during the extrusion process when thehydraulically settable mixture is compressed, the level of waterdeficiency will decrease, often dramatically. In some cases it mayapproach or even exceed 0%. (A negative water deficiency means that themis a surplus or excess of water; that is, the volume of water exceedsthe volume of interstitial voids between the solid particles after theyhave been compacted during the extrusion process.)

Nevertheless, hydraulically settable mixtures having a higher particlepacking density will generally be able to contain a greater deficiencyof water and yet be highly extrudable under pressure, as compared tomixtures which have a lower particle packing density. For example, whilethe particle packing density of a hydraulically settable mixture havinga natural packing density of 50% might increase to 65%, one with apacking density of 80% might increase to 95%. The drop in interstitialspace in the former case (50% to 35%) is slight compared to in thelatter (20% to 5%), which is a four-fold decrease. Hence, the mixturewith the higher particle packing density will experience a much moredramatic drop in the apparent water deficiency.

In some cases, it may also be preferable to add "excess water" or morewater than is needed to fill the interstitial space in order to decreasethe viscosity and increase the workability of the mixture. However, inorder to obtain immediate green strength, it may be necessary in thosecases to heat the surface of the extruded article using a heated die inorder to remove some or all of the "excess water." In addition, gypsumhemihydrate may be added to react with some or all of the excess waterand thereby increase the form stability of the extruded article.

In the case where more water or dispersant is added initially in orderto give the hydraulically settable mixture greater workability,increased form-stability of the extruded object or shape can be obtainedby, for example, immediately passing the object through a heating tunnelor vacuum chamber. This causes part of the water to be driven off in theform of vapor or steam from the article surface, which reduces thevolume of interstitial water, increases the friction between theparticles, and results in a quick increase in form-stability. However,overheating the extruded article, or drying it out too quickly, may harmthe microstructure of the article, thereby reducing the strength of thearticle.

E. Rheology-modifying Agents.

The inclusion of a rheology-modifying agent acts to increase the plasticor cohesive nature of the hydraulically settable mixture so that itbehaves more like a moldable or extrudable clay. The rheology-modifyingagent tends to thicken the hydraulically settable mixture by increasingthe yield stress of the mixture without greatly increasing the viscosityof the mixture. Raising the yield stress in relation to the viscositymakes the material more plastic-like (or clay-like) and moldable, whilegreatly increasing the subsequent form-stability or green strength.

A variety of natural and synthetic organic rheology-modifying agents maybe used which have a wide range of properties, including high or lowviscosity, yield stress, and solubility in water. Although many of therheology-modifying agents contemplated by the present invention might bevery soluble in water, the insoluble reaction products of hydrauliccement and water encapsulate the rheology-modifying agent and prevent itfrom dissolving out of an extruded hydraulically settable article thatis exposed to water.

The various rheology-modifying agents contemplated by the presentinvention can be roughly organized into the following categories: (1)polysaccharides and derivatives thereof, (2) proteins and derivativesthereof, and (3) synthetic organic materials. Polysacchariderheology-modifying agents can be further subdivided into (a)cellulose-based materials and derivatives thereof, (b) starch-basedmaterials and derivatives thereof, and (c) other polysaccharides.

Suitable cellulose-based rheology-modifying agents include, for example,methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose,hydroxypropylmethylcellulose, etc. The entire range of possiblepermutations is enormous and cannot be listed here, but other cellulosematerials which have the same or similar properties as these would alsowork well.

Suitable starch-based materials include, for example, amylopectin,amylose, seagel, starch acetates, starch hydroxyethyl ethers, ionicstarches, long-chain alkylstarches, dextrins, amine starches, phosphatestarches, and dialdehyde starches.

Other natural polysaccharide based rheology-modifying agents include,for example, alginic acid, phycocolloids, agar, gum arabic, guar gum,locust bean gum, gum karaya, and gum tragacanth.

Suitable protein-based rheology-modifying agents include, for example,Zein® (a prolamine derived from corn), collagen derivatives extractedfrom animal connective tissue such as gelatin and glue, and casein (theprincipal protein in cow's milk).

Finally, suitable synthetic organic plasticizers include, for example,polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol,polyvinylmethyl ether, polyacrylic acids, polyacrylic acid salts,polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides,ethylene oxide polymers, polylactic acid, synthetic clay, and latex,which may be a styrene-butadiene copolymer. The rheology of polylacticacid is significantly modified by heat and could be used alone or incombination with any other of the foregoing rheology-modifying agents.

A currently preferred rheology-modifying agent ismethylhydroxyethylcellulose, examples of which are Tylose® FL 15002 andTylose® 4000, both of which are available from HoechstAktiengesellschaft of Frankfurt, Germany. Lower molecular weightrheology-modifying agents such as Tylose® 4000 generally act toplasticize or lubricate the mixture rather than thicken it, which aidsin flowability during the extrusion procedure. Another usefulrheology-modifying agent is hydroxypropylmethylcellulose, which is soldunder the tradename of Methocel®.

More particularly, lower molecular weight rheology-modifying agentsimprove the extrusion process by lubricating the particles. This reducesthe friction between the particles as well as between the mixture andthe adjacent extruder surfaces. Although a methylhydroxyethylcelluloserheology-modifying agent is preferred, almost any non-toxicrheology-modifying agent (including any listed above) which imparts thedesired properties would be appropriate.

Another preferred rheology-modifying agent that can be used instead of,or in conjunction with, Tylose® or Methocel® is polyethylene glycolhaving a molecular weight of between 20,000 and 35,000. Polyethyleneglycol works more as a lubricant and adds a smoother consistency to themixture. For this reason, polyethylene glycol might be referred moreprecisely as a "plasticizer." In addition, it gives the extrudedhydraulically settable material a smoother surface. Stearates can alsobe added to lubricate the hydraulically settable mixture.

Finally, starch-based rheology-modifying agents are of particularinterest within the scope of the present invention because of theircomparatively low cost compared to cellulose-based rheology-modifyingagents such as Tylose® or Methocel®. Although starches typically requireheat and/or pressure in order to gelate, starches may by modified andprereacted so that they can gel at room temperature. The fact thatstarches, as well as many of the other rheology-modifying agents listedabove, have a variety of solubilities, viscosities, and rheologiesallows for the careful tailoring of the desired properties of a mixdesign so that it will conform to the particular manufacturing andperformance criteria of the desired extruded article.

The rheology-modifying agents within the hydraulically settablematerials of the present invention are preferably included in a rangefrom about 0.1% to about 5% by weight of the hydraulically settablemixture exclusive of water, more preferably in a range from about 0.25%to about 2%, and most preferably in a range from about 0.5% to about 1%.The actual amount to be used will depend upon the nature of the extrudedarticle or product.

F. Aggregates.

Aggregates common in the concrete industry may be used in thehydraulically settable mixtures of the present invention. In the casewhere relatively thin-walled articles will be extruded, and in order forthe mixtures to remain extrudable through the reduced cross-sectiondies, the diameter of the aggregates used will most often be less thanabout 25% of the smallest cross-section of the structural matrix of theextruded article.

Aggregates may be added to increase the compressive strength, decreasethe cost by acting as a filler, and affect the particle packing densityof the resultant hydraulically settable materials. Aggregates are alsouseful for creating a smooth surface finish, particularly plate-likeaggregates. The tensile and compressive strengths of the aggregate willoften affect the tensile and compressive strengths of the final hardenedproduct.

Examples of useful aggregates include sand, dolomite, gravel, rock,bauxite, basalt, granite, limestone, sandstone, glass beads, aerogels,xerogels, seagel, mica, clay, synthetic clay, alumina, silica, fly ash,silica fume, tabular alumina, kaolin, glass microspheres, ceramicspheres, gypsum dihydrate, calcium carbonate, calcium aluminate,xonotlite (a crystalline calcium silicate gel), unreacted cementparticles, and other geologic materials. Both hydrated and unhydratedcement particles may also be considered to be "aggregates" in thebroadest sense of the term, depending on their distribution and thenature of their incorporation within the hydraulically settable matrix.Even discarded hydraulically settable materials, such as discardedsheets, containers, boards, or other objects of the present inventioncan be employed as aggregate fillers and strengtheners. Silica fume andfly ash also can be added to reduce the porosity of the hydraulicallysettable mixture and increase its workability and cohesiveness.

The amount of the aggregate will vary depending upon the particularapplication or purpose, and can vary greatly from no added aggregate upto about 90% by weight of the green hydraulically settable mixture, morepreferably within the range from between about 3% to about 70% byweight, and most preferably from between about 20% to about 50% byweight.

Both clay and gypsum are particularly important aggregate materialsbecause of their ready availability, extreme low cost, workability, andease of formation. Gypsum hemihydrate can also provide a degree ofbinding and strength if added in high enough amounts. Clay is a generalterm used to identify all earths that form a paste with water and hardenwhen dried. The predominant clays include silica and alumina (used formaking pottery, tiles, brick, and pipes) and kaolinite. The twokaolinitic clays are anauxite, which has the chemical formula Al₂O₃.3SiO₂ •2H₂ O, and montmorillonite, which has the chemical formula Al₂O₂ •4SiO₂ •H₂ O. However, clays may contain a wide variety of othersubstances such as iron oxide, titanium oxide, calcium oxide, zirconiumoxide, and pyrite.

In addition, although clays have been used for millennia and can obtainhardness even without being fired, such unfired clays are vulnerable towater degradation and exposure, are extremely brittle, and have lowstrength. Nevertheless, clay makes a good, inexpensive aggregate withinthe hydraulically settable structural matrix.

Similarly, gypsum hemihydrate is also hydratable and forms the dihydrateof calcium sulfate in the presence of water. Thus, gypsum may exhibitthe characteristics of both an aggregate and a binder depending onwhether (and in what proportion) the hemihydrate or dihydrate form isadded to the hydraulically settable mixture.

It is often preferable, according to the present invention, to include aplurality of differently sized and graded aggregates capable of morecompletely filling the interstices between the aggregate andhydraulically settable binder particles. Optimizing the particle packingdensity reduces the amount of water necessary to obtain adequateworkability by eliminating spaces which would otherwise be filled withinterstitial water, often referred to as "capillary water." In addition,using less water increases the strength of the final hardened product(according to the Strength Equation).

In order to optimize the packing density, differently sized aggregateswith particle sizes ranging from as small as about 0.01 microns to aslarge as about 4 mm may be used. (Of course, the desired purpose andthickness of the resulting product will dictate the appropriate particlesizes of the various aggregates to be used.)

In certain preferred embodiments of the present invention, it may bedesirable to maximize the amount of the aggregates within thehydraulically settable mixture in order to maximize the properties andcharacteristics of the aggregates (such as qualities of strength, lowdensity, or high insulation). The use of particle packing techniques maybe employed within the hydraulically settable material in order tomaximize the amount of the aggregates.

A detailed discussion of particle packing can be found in the followingarticle coauthored by one of the inventors of the present invention:Johansen, V. & Andersen, P. J., "Particle Packing and ConcreteProperties," Materials Science of Concrete II at 111-147, The AmericanCeramic Society (1991). Further information is available in the DoctoralDissertation of Andersen, P. J., "Control and Monitoring of ConcreteProduction--A Study of Particle Packing and Rheology," The DanishAcademy of Technical Sciences. For purposes of teaching particle packingtechniques, the disclosures of the foregoing article and thesis areincorporated herein by specific reference.

A detailed description of how to select a mixture of aggregates andaggregate particle sizes to accommodate a given mix design criteria canbe found within co-pending U.S. patent application Ser. No. 08/109,100,filed Aug. 18, 1993, in the names of Per Just Andersen, Ph.D. and SimonK. Hodson for "Design Optimized Compositions And Processes ForMicrostructurally Engineering Cementitious Mixtures." For purposes ofdisclosure, this reference is incorporated herein by specific reference.

G. Fibers.

As used in the specifications and appended claims, the terms "fibers","discontinuous fibers", and "fibrous materials" include both inorganicfibers and organic fibers. Fibers are a particular kind of aggregatewhich may be added to the hydraulically settable mixture to increase thecohesion, elongation ability, deflection ability, toughness, fractureenergy, and flexural, tensile, and even compressive strengths. Fibrousmaterials reduce the likelihood that the extruded hydraulically settableobject will shatter when a strong cross-sectional force is applied.

Fibers which may be incorporated into the structural matrix arepreferably naturally occurring fibers, such as cellulosic fibersextracted from hemp, cotton, sisal, plant leaves, wood or stems, orfibers made from glass, polyvinyl alcohol, synthetic fibers (e.g.,Kevlar (polyaramide) and polypropylene fibers), silica, ceramic, ormetal. Glass fibers are preferably pretreated to be alkali resistant.

Preferred fibers include glass fibers, synthetic fibers, abaca, bagasse,wood fibers (both hardwood or softwood, such as southern hardwood orsouthern pine), ceramic fibers (such as alumina, silica nitride, silicacarbide, and graphite), and cotton. Recycled paper fibers can be used,but they are somewhat less desirable because of the fiber degradationthat occurs during the original paper manufacturing process, as well asin the recycling process. Any equivalent fiber, however, which impartsstrength and flexibility is also within the scope of the presentinvention. Abaca fibers are available from Isarog Inc. in thePhilippines. Glass fibers, such as Cemfill®, are available fromPilkington Corp. in England.

The fibers used to make the hydraulically settable materials of thepresent invention preferably have a high length to width ratio (or"aspect ratio") because longer, narrower fibers can impart more strengthto the matrix without significantly adding bulk and mass to the mixture.The fibers should have an aspect ratio of at least about 10:1,preferably at least about 100:1, and most preferably at least about200:1. However, although the toughness and tensile strength of the finalproduct are increased as the aspect ratio of the fibers is increased,fibers with lower aspect ratios are cheaper, provide better particlepacking, and are easier to disperse within the hydraulically settablemixture.

The amount of fibers added to the hydraulically settable matrix willvary depending upon the desired properties of the final product, withstrength, toughness, flexibility, and cost being the principal criteriafor determining the amount of fiber to be added in any mix design. Inmost cases, fibers will be added in an amount within a range from about0.5% to about 30% by volume of the green hydraulically settable mixture,more preferably within the range from about 1% to about 20% by volume,and most preferably within the range from about 2% to about 10% byvolume. The extrusion process tends to longitudinally orient the fibersand results in a tougher product.

It will be appreciated, however, that the strength of the fiber is avery important feature in determining the amount of the fiber to beused. The stronger the tensile strength of the fiber, the less theamount that must be used to obtain the same level of tensile strength inthe resulting product. Of course, while some fibers have a high tensilestrength, other types of fibers with a lower tensile strength may bemore elastic. Hence, a combination of two or more fibers may bedesirable in order to obtain a resulting product that maximizes multiplecharacteristics, such as high tensile strength and high elasticity.

In addition, while ceramic fibers are generally far more expensive thannaturally occurring or glass fibers, their use will nevertheless beeconomical in some cases due to their far superior tensile strengthproperties. Obviously the use of more expensive fibers becomes moreeconomical as the cost restraints of the extruded object are relaxed,such as where a comparable object made from a competing material isrelatively expensive.

It should also be understood that some fibers, such as southern pine andabaca, have high tear and burst strengths, while others, such as cotton,have lower strength but greater flexibility. In the case where bothflexibility and high tear and burst strength is desired, a mixture offibers having the various properties can be added to the mixture.

The strength properties of the fiber impregnated hydraulically settablematrix are substantially different depending on whether the fibers are"mechanically anchored" or "chemically anchored" within the matrix. Theterm "mechanically anchored" refers to a primarily mechanicalinteraction between the fibers and the other components of thehydraulically settable matrix such that the bond or interface betweenthe fiber and the hydraulically settable matrix is generally weaker thanthe strength of the fibers. As a result, when a strain is applied to theextruded article, there will generally be a "pull-out" of the fibersfrom their spacial position within the hydraulically settable matrixrather than a rupture of the fibers. This pull-out effect, and theattendant frictional energy transferred during slippage, increases thetoughness and fracture energy of the extruded article in part because ofthe bridging by the fibers of any cracks caused by the strain on theextruded article, and also because the randomly oriented fibersdispersed within the hydraulically settable matrix create a much longerpath of crack propagation throughout the matrix. However, because of thepull-out effect of mechanically anchored fibers, they would not beexpected to substantially increase the tensile and flexural strength ofthe extruded article. As set forth more fully below, the tensile andflexural strengths of the extruded articles of the present invention aremore dramatically increased by the filaments placed within the extrudedarticle.

In contrast to mechanically anchored fibers, the term "chemicallyanchored" refers to a primarily chemical interaction between the fibersand the other components of the hydraulically settable matrix such thatthe bond or interface between the fiber and the hydraulically settablematrix is generally stronger than the strength of the fibers. As aresult, when a strain is applied to the extruded article, there will notbe a "pull-out" effect of the fibers but rather the fibers will remainsecurely anchored within the hydraulically settable matrix until thestress on the article causes the article to fail. At the moment that theextruded article fails, the chemically anchored fibers will rupture. Theresult is that chemically anchored fibers are able to significantlyincrease the tensile strength (i.e., the peak load before failure) andflexural strength of the extruded article. However, chemically anchoredfibers do not increase the toughness of the extruded article, which willgenerally experience a catastrophic failure at the peak load.

Increasing the chemical similarity of the fibers compared to thehydraulically settable binder increases the tendency of the fiber to bechemically anchored within the hydraulically settable matrix. This maybe achieved, for example, by coating a variety of fibers withprecipitated silica or ettringite. Also, both glass and alumina fiberswill tend to be more chemically anchored compared to, for example,Kevlar or polypropylene fibers. In many cases it may be desirable toobtain the beneficial effect of both chemical and mechanical anchoringof the fibers by adding a mixture of different fibers.

H. Filaments.

The terms "filaments", "continuous filaments" or "continuous fibers" asused in this specification and the appended claims are intended toinclude individual continuous fibers or continuous assemblages of eitherdiscontinuous or continuous fibers introduced into the hydraulicallysettable mixture during the extrusion process. Filaments are to bedistinguished from discontinuous or chopped fibers, which are mixed intothe hydraulically settable mixture and which generally have a randomorientation (although there may be some alignment of the fibers as aresult of the extrusion process).

Placement of continuous filaments into the hydraulically settable matrixanchors the filaments over a substantially longer distance thandiscontinuous fibers imparts substantially different properties to thefinal hardened article than short fibers. Filaments within thehydraulically settable structural matrix substantially increases thetensile, flexural, and hoop or circumferential strengths of the hardenedhydraulically settable article, depending on the orientation of thefilaments. Filaments placed within a hydraulically settable structuralmatrix also tend to increase the toughness and elongation ability of thehydraulically settable article. Preferred filaments will have sufficienttensile and shear strengths to independently contribute to the strengthof the article.

The "pull-out" effect of filaments tends to be minimal as filaments areanchored within substantial lengths of an article, which makes itdifficult for the filaments to be dislodged. As a result of the minimal"pull-out" effect, the difference between filaments which aremechanically anchored and filaments which are chemically anchored isless significant than for discontinuous fibers.

Any type of filaments, including inorganic fibers and organic fibers,can be positioned within a hydraulically settable mixture and can have awidth or thickness corresponding to the desired strength, length,thickness, or other properties of the extruded article. The filamentscan be placed in the hydraulically settable matrix as an individualfilament or as a continuous assemblage of continuous or discontinuousfibers. Any assemblage of filaments can be utilized including theconventional assemblages such as a "strand" which is an assemblage ofuntwisted filaments, a "yarn" which is an assemblage of twistedfilaments, a "roving" which is a collection of bundles of filamentseither as untwisted strands or as twisted yarns, a "tow" which is anuntwisted bundle of strands or a "mat" which is a sheet of filaments.

The number or volume of filaments placed into the hydraulically settablematrix will vary depending upon the desired properties of the finalproduct, with strength, toughness, flexibility, and cost being theprincipal criteria for determining the amount of filament to be added inany product design. Typically, the volume of filament in an article willbe in a range between about 0.5% to about 30% of the volume of thehydraulically settable structural matrix. The volume of filament is morepreferably within the range from about 1% to about 20%. The volume offilament is most preferably within the range from about 2% to about 10%.

It will be appreciated, however, that the strength of the filament is avery important feature in determining the amount of the filament to beused. The stronger the tensile strength of the filament, the less theamount that must be used to obtain the same level of tensile strength inthe resulting product. Of course, while some filaments have a hightensile strength, other types of filaments with a lower tensile strengthmay be more elastic. Hence, a combination of two or more filaments maybe desirable in order to obtain a resulting product that maximizesmultiple characteristics, such as high tensile strength and highelasticity.

Additionally, the volume of filament needed to obtain the desiredproperties is affected by the manner in which the filament is placedwithin the hydraulically settable structural matrix during extrusion.The filaments can be placed within the hydraulically settable structuralmatrix to have several different configurations and can be placed atvarying depths from the surface of the article. To obtain an anisotropicarticle having strength in the extrusion direction, the filaments can beplaced parallel to each other extending within the article along thesame axis as the extrusion direction. The volume of fiber needed canalso be reduced by placing the filament in a criss-cross pattern as thearticle is being extruded by helically winding filament in oppositedirections. Additionally, the filaments can be placed in both a parallelconfiguration and a helical configuration in order to obtain thebeneficial effects of both.

Common types of continuous fibers used with the present inventioninclude fiberglass, polyaramid fibers, graphite fibers, carbon fibers,polyethylene fibers and other organic fibers. Fiberglass is often usedbecause of its low cost, dimensional stability, good impact properties,moderate strength and modulus, and ease of handling. Polyaramid fibers,commonly referred to as Kevlar®, have a very high specific strength ormodulus but have relatively poor shear and compression properties.Polyaramid fibers are often used in pressure vessels, as they avoidshear and compressive stresses. The largest variety of availablestrengths and moduli can be obtained with graphite fibers which, for aprice, can be designed to meet most parameters. The above filaments canbe purchased from companies such as Hercules Aerospace Co. of Magna,Utah; 3-M of St. Paul, Minn.; Owens-Corning Fiberglass of Toledo, Ohio;Pittsburg Plate Glass, Manville Co.; Vetrotex St. Gobain; DuPont; AlliedFibers, and Amoco.

Alternatively, filaments can be made from natural organic fibers such ascotton, hemp, and jute. Although such fibers have a relatively lowtensile strength, they are far less expensive than fiberglass,polyaramid, or graphite fibers. Natural organic fibers may thus be moreeconomical in articles that will be subjected to lower stresses.

I. Dispersants.

The term "dispersant" is used hereinafter to refer to the class ofmaterials which can be added to reduce the amount of water that must beadded in order to maintain the same flow properties. Dispersantsgenerally work by reducing the viscosity and yield stress of thehydraulically settable mixture. A more detailed description of the useof dispersants may be found in the Master's Thesis of Andersen, P. J.,"Effects of Organic Superplasticizing Admixtures and Their Components onZeta Potential and Related Properties of Cement Materials" (1987). Forpurposes of disclosure, the above-referenced article is incorporatedherein by specific reference.

Dispersants generally work by being adsorbed onto the surface of thehydraulically settable binder particles and/or into the near colloiddouble layer of the binder particles. This creates a negative chargearound the surfaces of particles, causing them to repel each other. Thisrepulsion of the particles adds "lubrication" by reducing the "friction"or attractive forces that would otherwise cause the particles to havegreater interaction. Because of this, less water can be added initiallywhile maintaining the workability of the hydraulically settable mixture.

Greatly reducing the viscosity and yield stress may be desirable whereclay-like properties, cohesiveness, and/or form-stability are lessimportant or where it is desired to use less water initially. Adding adispersant aids in keeping the hydraulically settable mixture workableeven when very little water is added, particularly where there is a"deficiency" of water. Hence, adding a dispersant allows for an evengreater deficiency of water, although the extruded article may havesomewhat less form-stability if too much dispersant is used.Nevertheless, including less water initially will theoretically yield astronger final cured article, according to the Strength Equation.

Whether or not there is a deficiency of water is both a function of thestoichiometric amount of water required to hydrate the binder and theamount of water needed to occupy the interstices between the particlesin the hydraulically settable mixture, including the hydraulicallysettable binder particles themselves and the particles within theaggregate material and/or fibrous material. As stated above, improvedparticle packing reduces the volume of the interstices between thehydraulically settable binder and aggregate particles and, hence, theamount of water necessary to fully hydrate the binder and maintain theworkability of the hydraulically settable mixture by filling theinterstitial space.

However, due to the nature of the coating mechanism of the dispersant,the order in which the dispersant is added to the mixture is oftencritical. If a flocculating/gelating agent such as Tylose® or starch isadded, the dispersant must be added first and the flocculating agentsecond. Otherwise, it will be more difficult for the dispersant tobecome adsorbed on the surface of the hydraulically settable binderparticles, as the Tylose® or starch may become irreversibly adsorbedonto the surface of the particles, thereby bridging them together ratherthan causing them to repel each other.

A preferred dispersant is sulfonated naphthalene-formaldehydecondensate, an example of which is WRDA 19, which is available from W.R. Grace, Inc., located in Baltimore. Other dispersants which would workwell include sulfonated melamineformaldehyde condensate, lignosulfonate,and acrylic acid. The sodium salt of sulfonated naphthalene-formaldehydecondensate can be added after the hydraulic cement and water have hadsufficient time to form early hydration products (such as ettringite) inorder to increase the specific surface area of the cement particles,which allows for greater dispersion of the particles.

Another way to improve the flowability of the hydraulically settablemixture under lower pressure is by adding other reactive products havinga high specific surface area, such as silica fume. This also increasesthe yield stress and, hence, the form-stability of the extruded article.

The amount of added dispersant will generally range up to about 5% byweight of the hydraulically settable binder, more preferably within therange of between about 0.25% to about 4%, and most preferably within therange of between about 0.5% to about 2%. However, it is important not toinclude too much dispersant, as it tends to retard the hydrationreactions between, e.g., hydraulic cement and water. Adding too muchdispersant can, in fact, prevent hydration, thereby destroying thebinding ability of the hydraulic paste altogether.

The dispersants contemplated within the present invention have sometimesbeen referred to in the concrete industry as "superplasticizers," "waterreducers," or "high range water reducers." In order to betterdistinguish dispersants from rheology-modifying agents, which often actas plasticizers, the term "superplasticizer" will not be used in thisspecification.

J. Set Accelerators.

In some cases, it may be desirable to accelerate the initial set of thehydraulically settable mixture and obtain earlier form stability of theextruded article by adding to the mixture an appropriate setaccelerator. These include Na₂ CO₃, KCO₃, KOH, NaOH, CaCl₂, CO₂,triethanolamine, aluminates, and the inorganic alkali salts of strongacids, such as HCl, HNO₃, and H₂ SO₄. In fact, any compound whichincreases the solubility of gypsum and Ca(OH)₂ will tend to acceleratethe initial set of hydraulically settable mixtures, particularlycementitious mixtures.

The amount of set accelerator which may be added to a particularhydraulically settable mixture will depend upon the degree of setacceleration that is desired. This in turn will depend on a variety offactors, including the mix design, the time interval between the stepsof mixing the components and molding or extruding the hydraulicallysettable mixture, the temperature of the mixture, and the identity ofthe set accelerator. One of ordinary skill in the art will be able toadjust the amount of added set accelerator according to the parametersof a particular manufacturing process in order to optimize the settingtime of the hydraulically settable mixture.

K. Coatings.

It is within the scope of the present invention to coat the extrudedhydraulically settable objects with scaling materials, paints, and otherprotective coatings. Appropriate coatings include calcium carbonate,melamine, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate,polyacrylate, hydroxypropylmethylcellulose, polyethylene glycol,acrylics, polyurethane, polyethylene, synthetic polymers, polylacticacid, Biopol® (a polyhydroxybutyrate-hydroxyvalerate copolymer), waxes(such as beeswax or petroleum-based wax), elastomers, kaolin clay,polyacrylates, and synthetic polymers, including biodegradable polymers.Biopol® is manufactured by ICI in the United Kingdom.

For example, a coating comprised of sodium silicate, which is watersoluble (pH=7) but acid resistant, is a particularly useful coating.Resistance to acidity is important, for example, where an extruded pipewill be used to transport, e.g., aqueous acids. Where it is desirable toprotect the extruded article from basic substances, the article may becoated with an appropriate polymer or wax, such as are used to coatpaper or paperboard products. If the extruded articles are intended tocome into contact with foodstuffs the coating material will preferablycomprise an FDA-approved coating.

The coatings may be applied to the extruded articles using any coatingmeans known in the art. Coatings may be applied by spraying the extrudedobject with any of the above-referenced coating materials, or it may beadvantageous to apply the coating by dipping the article into a vatcontaining an appropriate coating material. In the case where a coatingmaterial is sprayed onto the surface of a generally flat or regularlycurved object, the coating material may be spread or smoothed by meansof a straight or curved doctor blade which is held a particular distanceabove the object, or which rides directly on the surface. In addition,coatings may be coextruded along with the extruded object in order tointegrate the coating process with the extrusion process.

II. EXTRUDING HYDRAULICALLY SETTABLE MIXTURES.

The basic structural component of the extruded articles of the presentinvention is the hydraulically settable matrix, which is formed from thereaction products of a hydraulically settable binder and water. Withinthe basic structural matrix are incorporated other components which addadditional characteristics and properties, such as fibers, aggregates,rheology-modifying agents, dispersants, and set accelerators. Using amicrostructural engineering and materials science approach makespossible the ability to include these various ingredients in a varietyof amounts and proportions in order to build into the mixture thedesired properties of form-stability and ultimate strength, toughness,and other performance criteria of the final hardened product.

The basic steps involved in the extrusion of hydraulically settablemixtures are as follows: (1) choosing the desired qualities andattributes of the article to be extruded from a hydraulically settablemixture, including size and strength properties; (2) selecting thedesired parameters of an appropriate extrusion process, including thetype of extruder, the die orifice shape, and the extrusion pressure,speed, and temperature; (3) determining the optimum composition andrheology, or range of rheologies, of an appropriate hydraulicallysettable mixture tailored to the desired qualities and attributes of thearticle and the desired parameters of the extrusion process; (4)preparing a suitable hydraulically settable mixture having theappropriate composition and rheology; (5) extruding the hydraulicallysettable mixture into the desired articles, or precursors to articlesthat can be further shaped into the desired articles; and (6) allowingthe extruded article, or later shaped article, to harden into the finalcured article. Optionally, the curing process may be accelerated by, forexample, autoclaving or by placing a partially hardened article into ahigh humidity environment.

A. Designing the Desired Qualities of the Article.

Using the compositions and methods set forth herein, a wide variety ofarticles may be mass produced in high volume by extruding ahydraulically settable mixture into the desired shape of the article, orinto a precursor shape that may be further shaped into the desiredarticle. The articles formed by using the extrusion methods of thepresent invention are characterized as having high compressive, tensile,and flexural strength, as well as high particle packing density of thesolid aggregate and hydraulically settable binder particles. Thisresults in a more dense and less porous hydraulically settable materialthan has been heretofore possible. This, in turn, results in an articlehaving low penetrability and low diffusion of moisture. Thesecharacteristics are possible using a microstructural engineeringapproach in order to design into the material beforehand the desiredproperties and performance criteria.

The high particle packing density of the extruded articles results from(1) the selection of aggregate particles having a predetermineddistribution of sizes and shapes in order to optimize the naturalparticle packing density, and (2) the extrusion of the hydraulicallysettable material under generally high pressures, which force theparticles into an even higher packing density than the natural packing,particularly where there is an initial deficiency of water.

The high particle packing density and low water to hydraulicallysettable binder ratio that results from having an initial deficiency ofwater yield extruded articles having very low porosity and, hence, highstrength according to the Strength Equation. The use of dispersantsallows for the inclusion of even less water initially in order to createa more water deficient hydraulically settable mixture which will,nevertheless, be capable of being extruded under pressure.

The type of aggregate that will be used will depend largely on thedesired strength and density criteria of the final cured article, aswell as cost. Aggregates such as crushed sand, crushed granite, crushedbasalt, silica, gypsum, and clay are extremely inexpensive and cangreatly reduce the cost of manufacturing an extruded article therefrom.Such aggregates are also characterized as having high density and highcompressive strength.

The inclusion of a hydraulically settable binder such as portland greyor portland white cement will yield a final cured product that isgenerally waterproof and which will resist penetration by water andother liquids. Nevertheless, other hydraulically settable binders, suchas gypsum hemihydrate, are less water resistant and will yield a finalcured article having lower resistance to water. In the event that a morewater resistant article is desired, it may be advantageous to apply anappropriate coating onto the surface of the extruded article.

The inclusion of fibers and filaments and other high strength fillerscan greatly increase the tensile, flexural or hoop strengths of thefinal cured articles. The tensile strength may be stronger along one ormore vectors or be evenly distributed depending on whether the fibersare aligned or randomly dispersed throughout the hydraulically settablematrix and whether the filaments are parallel or helical within thestructural matrix. The extrusion process itself will tend to orient thefibers in the direction of extrusion.

Different fibers and filaments have greatly varying degrees of tear andburst strength, flexibility, tensile strength, ability to elongatewithout breaking, and stiffness. The type of fiber that will beincorporated into the hydraulically settable material will depend on thedesired properties of the article. In order to obtain the advantageousproperties of different types of fibers it may be preferable in somecases to combine two or more different kinds of fibers within thehydraulically settable material.

In light of the foregoing, the cured extruded articles will preferablyhave a tensile strength greater than about 15 MPa. In many cases,depending on the mix design, water content, and extrusion pressure, itwill be possible to obtain extruded articles having tensile strengths ofabout 30 MPa or greater and, in some cases, of about 50 MPa or greater.Because of the ability to remove a large percentage of the interstitialvoids which are normally found within most cementitious products, thecured extruded hydraulically settable materials of the present inventionwill have a tensile strength to compressive strength ratio of about 1:7,which is higher than conventional concrete products, which typicallyhave a tensile strength to compressive strength ratio of only about1:10. Moreover, where high tensile strength fibers are employed insufficient quantities, it is possible, according to the presentinvention, to obtain cured hydraulically settable materials which have atensile strength to compressive strength ratio of about 1:3.

Because of the ability to extrude relatively thin-walled articles havingrelatively large internal cavities, it is possible for such extrudedarticles to have relatively low bulk densities. Extruded articles havinga multicellular structure will preferably have a bulk density less thanabout 1.5 g/cm³. Because of the ability to extrude multicellulararticles having wall thickness to cavity ratios that are far lower thanwhat is presently possible in the art, it is possible to extrudearticles having bulk densities of about 0.7 g/cm³ or lower and, in somecases, of about 0.3 g/cm³ or lower. Whether an extruded article willhave a lower, intermediate, or higher bulk density will generally dependon the desired performance criteria for a given usage, and will usuallydepend on the ratio of the volumes of the solid walls of the article andinternal cavities therein. The specific gravity of the solid walls ofthe articles will generally remain within the ranges stated herein.

In light of the foregoing, the extruded articles of the presentinvention will usually have significantly higher tensile strength tobulk density ratios compared to prior art cementitious articles. Theextruded articles will preferably have a tensile strength to bulkdensity ratio greater than about 5 MPa-cm³ /g, more preferably greaterthan about 15 MPa-cm³ /g, and most preferably greater than about 30MPa-cm³ /g.

B. Selecting the Extrusion Process.

The type of extrusion process that will be employed will vary dependingon the nature of the hydraulically settable mixture being extruded, aswell as the desired properties of the extruded article. Although thehydraulically settable mix designs of the present invention havecarefully controlled theology and plastic-like properties, which makethem suitable for other molding processes, the essential feature of theproducts of the present invention is that they can be continuouslyextruded into extruded articles that are form-stable immediately or veryshortly after the extrusion process. The continuous nature of extrusionprocess allows for the formation of a wide variety of articles in aneconomical and inexpensive fashion.

As stated above, a combination of particle packing density, waterdeficiency, and compression during the extrusion process creates ahydraulically settable mixture with a discontinuous theology. Animportant criterion in the extrusion process is providing an extrudercapable of exerting the proper pressure or range of pressures for agiven mix design. Pressure within the proper range is necessary in orderto increase the particle packing density, and concomitantly decrease thevolume of interstitial space, which decreases the effective waterdeficiency of the mixture. This allows for better lubrication of theparticles and increased workability and flow properties.

The best properties are generally obtained by exerting a pressure whichis commensurate with the levels of particle packing, water deficiency,and aggregate strength within the mixture. Too little pressure might beinadequate to impart adequate flow properties to the hydraulicallysettable mixture. Conversely, too much pressure may pulverize certainaggregates within the hydraulically settable mixture, while compressingthe mixture to the point of having excess water. Excess water may, insome cases, reduce the viscosity and/or yield stress of thehydraulically settable mixture to the point that it will lack sufficientform-stability.

Depending on the amount of pressure that is desired and the amount ortype of shear to be exerted onto the hydraulically settable mixture,either a piston-type or auger-type extruder can be used. The advantageof the piston-type extruder is the greater amount of pressure which canbe applied. In order to apply very high pressures, including those of upto 100,000 psi, the only current possibility is to use a pistonextruder.

Auger-type extruders typically do not exert as much pressure as a pistonextruder, and are preferred where extremely high pressures areunnecessary. Auger-type extruders have the advantage of impartinginternal shear by the turning of the auger screw and the ability toapply a vacuum or negative pressure to the hydraulically settablemixture within the auger extruder to remove unwanted air within themixture on a more continuous basis. The double auger extruder has beenused mainly on an experimental basis and includes two parallel augerscrews, which allow for a wider extruder die and greater extrusionpressures. In most other respects, the twin auger extruder is similar tothe single auger extruder.

However, where hydraulically settable mixtures that are very deficientin water are used, it will often be necessary to use a piston extruderin order to exert higher pressures on the mixtures and cause them toflow. In such cases, the hydraulically settable mixture might appear asa dry-looking, granulate material prepared by mixing the componentswithin a drum. The granulates are placed into a piston extruder chamber,put under a vacuum, and then compacted under high pressure by the pistonin order to extrude the material. The use of a duel-batch pistonextruder allows for a semi-continuous extrusion process.

A currently preferred system for large scale mixing and extrusion in anindustrial setting involves equipment in which the materialsincorporated into the hydraulically settable mixture are automaticallyand continuously metered, mixed, de-aired, and extruded by either asingle or twin auger extruder apparatus. Either a single or twin augerextruder apparatus has sections with specific purposes, such as lowshear mixing, high shear mixing, vacuuming, and pumping. A single ortwin auger extruder apparatus has different flight pitches andorientations which permit the sections to accomplish their specificpurposes.

The main types of extruders include either the clay or the plastic orfood extruder. A clay extruder usually has an extruder having a veryhigh pitch and flight height, the pitch often being 90° from theextruder die. The high pitch increases the amount of surface area of theinterface between the auger blades and the material to be extruded, andincreasing the pitch and resulting surface area increases the pressureand shear rate of the extruder.

On the other hand, a plastic or food extruder has a much lower flightheight and pitch compared to the clay extruder. In this case, thepressure and shear rate are controlled by increasing or decreasing theRPM of the auger screw. Of course, increasing the RPM of the auger screwof a clay extruder will also increase the pressure and shear rate.

C. Designing The Hydraulically Settable Mixture.

The two main criteria used to design an appropriate hydraulicallysettable mixture are the desired rheology of the mixture before, during,and after the extrusion process and the desired properties of the finalhardened extruded article. As set forth above, the theology of thehydraulically settable mixture is preferably designed so that themixture will be able to flow and be extruded when subjected to theparameters of the given extrusion process, and thereafter be form-stableimmediately or shortly after being extruded.

1. Designing the Mixture Rheology.

As previously discussed, the rheology of the hydraulically settablemixture may be determined initially by controlling (1) the particlepacking density of the aggregate and hydraulically settable binderparticles, (2) the amount of added water, including the level of waterdeficiency, and (3) the identity and amount of any organic polymerrheology-modifying agents, plasticizers, or dispersants. How thesematerials and conditions are interrelated has been discussed in detail.

In addition, the rheology of the hydraulically settable mixture may bealtered by the addition of shear forces to effect shear thinning orpseudo-plastic behavior of the water deficient mixture, as well as bycompressive forces which reduce the level of water deficiency by forcingthe aggregate and hydraulically settable binder particles into closerproximity. In light of this, the level of water deficiency shouldcorrelate to the amount of compression and shear force that will beexerted on the hydraulically settable mixture. That is, less water may,as a general matter, be added initially as the amount of compressive andshear forces associated with the extrusion process are increased.

The release of the compressive and shear forces upon extruding thehydraulically settable mixture into the desired article results in aform-stable article held together by internal cohesion of the capillarywater or meniscuses. However, these internal forces are dependent uponthe amount of water within the capillaries of the material within theextruded article. If the amount of water is too low, there will beinsufficient capillary forces to maintain adequate cohesion. Conversely,if the amount of water is too high, the material will have inadequateyield stress to remain form-stable. The amount of water that remainswill be a function of the amount of water added initially, as well asthe level of compression during the extrusion process.

Upon hydrating, the extruded hydraulically settable material willdevelop its final strength properties. The compressive strength of thematerial may be determined by the Strength Equation, and is mainly afunction of the porosity of the final hardened material. This is alsotrue for the tensile and flexural strengths of the hardened material toa certain extent. Porosity can be reduced by increasing the initialparticle packing density and by decreasing the amount of water that isadded initially (or increasing the water deficiency). The level ofcompressive strength that is desired will depend on the particularperformance criteria of the desired article.

In addition, the compressive strength can be increased by using strongeraggregates. Conversely, lighter weight aggregates can be employed when aless strong, but lighter weight article is desired. The tensile andflexural strengths may be altered by adding varying amounts of fiber.Shorter, stronger fibers, such as ceramic fibers, will generally yield arelatively stiff final hardened article with high tensile and flexuralstrength. Other fibers, such as cellulosic fibers, have lower tensilestrength but are less expensive and more flexible and may be adequatewhere properties of flexibility and toughness are more important.

a. Optimizing the Particle Packing Density.

Achieving an optimized particle packing arrangement within the solidmaterials of the hydraulically settable mixture is desirable in order toobtain a hydraulically settable mixture having the desired theologicaland final strength properties. Once the particle packing density of adry mixture is determined, it is then possible to calculate how muchwater should be added to the mixture in order to achieve the desiredlevel of water deficiency. A detailed description of the theory, models,and steps necessary to accurately and reproducibly optimize theparticle-packing density of the solid particles with a hydraulicallysettable mixture is set forth in copending U.S. application Ser. No.08/109,100, entitled: "Design Optimized Compositions and Processes forMicrostructurally Engineering Cementitious Mixtures," and filed Aug. 18,1993, in the name of Per Just Andersen, Ph.D. and Simon K. Hodson (nowabandoned). For purposes of disclosure, this application is incorporatedherein by specific reference. In addition, mathematical and graphicmodels used to determine and quantify the particle-packing density of amixture is set forth in V. Johansen and P. J. Andersen, "ParticlePacking and Concrete Properties" at 118-22, Materials Science ofConcrete II (The American Ceramic Society, Inc., 1991). For purposes ofdisclosure, this article is incorporated herein by specific reference.

In order to achieve a desired packing density of the various particleswithin the hydraulically settable mixture, including the hydraulicallysettable binder particles and the aggregates, the particles will have atleast two size ranges. In order to increase the particle-packing densityto higher theoretical limits, it may be preferable in some cases to havethree or more different size ranges of particles. For purposes ofparticle packing, mixtures that contain two different size ranges ofparticles are referred to as "two-component systems", those that havethree different particle size ranges are referred to as "three-componentsystems", and so on. For simplicity, the two different components of atwo-component system may be referred to as the fine and coarsecomponents, while in the three-component system they may be referred asthe fine, medium, and coarse components.

In order to obtain an optimized level of particle packing, it ispreferable for the average particle size within one size range to be atleast seven and one-half times the particle size of the next smallestparticle range, more preferably at least about ten times, and mostpreferably at least about twelve and one-half times. (In many cases theratio may be greater.) For example, in a two-component system, it willbe preferable for the average particle size of the coarse component tobe at least about seven and one-half times the average particle size ofthe fine component. Likewise, in a three-component system, it will bepreferable for the average particle size of the coarse component to beat least seven and one-half times the average particle size of themedium component, which will likewise preferably be at least seven andone-half times the size of the fine component. Nevertheless, as moredifferently sized particles are added, the ratio between the particlesize magnitudes need not always be this great.

In a three-component system, it will be preferable for the fineaggregate particles to have diameters within a range from about 0.01microns to about 2 microns, with a medium aggregate particle to havediameters in a range from about 1 to about 20 microns, and for thecoarse aggregates to have a diameter within a range from about 100microns to about 2 mm. In a two component system, any two of theseranges may be preferable. Larger and smaller diameter particles may beused, as well as particles within different ranges, depending on thenumber of different particle types.

The term "type" as used in the specification and appended claims withregard to aggregate, hydraulically settable binder, and other solidparticles is intended to include both the kind of material used and theranges of the particle sizes. For example, although coarse aggregatesusually have particle diameters in a range from about 100 microns toabout 2 mm, one type of coarse aggregate may have a particle size rangefrom about 200 to about 500 microns while a second type may have aparticle size range from about 700 microns, to about 1.2 mm. As statedherein, optimal particle packing of a mixture can be obtained byselectively combining different types of aggregates. Each type ofaggregate has a defined average particle size; studies have found,however, that particle gap grading leads to good packing but lowworkability compared to continuous gradation.

In general, a two-component (or binary) packing system will seldom havean overall packing density higher than about 80%, while the upper limitfor a three-component (or ternary) system is about 90%. To obtain higherparticle packing, it will be necessary, in most cases, to add four ormore components, although having broader and more optimized particlesizes among two- or three-component systems can yield higher overallparticle packing than 80% and 90%, respectively.

The hydraulically settable binder used in the present invention isusually a hydraulic cement, gypsum, or calcium oxide and may, in somecases, comprise fly ash or silica fume. Hydraulic cement ischaracterized by the hydration products that form upon reaction withwater. Hydraulic cements generally have particle sizes ranging from 0.1μm to 100 μm. Portland cement, Type 1 has an average particle size in arange from about 10 to about 25 microns.

The types of aggregates and hydraulically settable binders used in thepresent invention are further defined by the average diameter size (d')and the natural packing density (φ) of the types of particles. Thesevalues are experimentally determined and are necessary for calculatingthe packing density of the resulting hydraulically settable mixture.

The natural packing density of each type of material is determined byfilling the material into a cylinder having a diameter of at least 10times the largest particle diameter of the material. The cylinder isthen tapped against a hard surface until the material is fullycompacted. By reading the height of compacted material in the cylinderand the weight of material, the packing density is calculated accordingto the formula: ##EQU1## Where, W_(M) =weight of the material,

SG_(M) =specific gravity of the material, and

V_(M) =volume of the material.

Of course, two or more types of hydraulically settable binder may alsobe added to a mixture. The particle size of the hydraulically settablebinder is usually so small, however, that the combination of differenttypes of hydraulically settable binders generally does not significantlyaffect the packing density of the mixture. Nevertheless, in somesituations the combination of different types of hydraulically settablebinders may be relevant. In these situations, the types of hydraulicallysettable binder can be represented as a pseudo-particle in the samemanner as for fine and coarse aggregate.

The above described process teaches a method for determining the packingdensity for all possible combinations of a given feed stock. With regardto the rheological effect, increasing the particle packing densityallows for the inclusion of less water while maintaining the same levelsof workability and plastic-like behavior of the mixture. In addition toimproving the rheological properties of the mixture while in the greenstate, maximizing particle packing density also increases the strengthof the final cured product by reducing the amount of interstitial spacefilled either by air, water, or a combination of both (according to theStrength Equation).

Nevertheless, it should be understood that "optimizing" the particlepacking system will not necessarily be achieved by simply maximizing theparticle packing density. As a general rule, maximization of particlepacking density tends to increase the desired properties which areachieved through particle packing. However, restraints such as costand/or availability of particular aggregates might warrant a lowerparticle packing density while still obtaining a mixture with adequaterheological properties for a particular purpose.

Although it has been recognized that increasing the particle packingdensity aids in controlling the rheological properties of ahydraulically settable mixture, the maximum packing density in the priorart has been about 65%. In contrast, through the particle packingtechniques described above, it is possible to obtain natural particlepacking densities greater than 65%, and even as high as 99%.

In general, the particle packing density will preferably be within arange from about 0.65 to about 0.99, more preferably between about 0.70and about 0.95, and most preferably between about 0.75 and about 0.90.(The added cost of achieving 99% particle packing efficiency is oftenprohibitive. Therefore, most preferred packing densities are somewhatless).

FIG. 1 illustrates the concept of particle packing by showing across-section of particles which have been efficiently packed together(particle packing density of 0.70). From FIG. 1, it can be seen that thespaces between the larger aggregate particles that would normally beoccupied by air are instead occupied by smaller aggregates. Moreover,the space between the larger and smaller particles which would normallybe occupied by air are in turn occupied by yet smaller sized aggregateparticles. In this way, the volume of interstitial air between theparticles is greatly reduced, while the particle packing density isgreatly increased.

FIG. 2 graphically illustrates and quantifies the actual packing densityby showing how in a typical packing system (particle packing density of0.70) the overall volume of the mixture is distributed between solidparticles (70%) and interstitial space (30%). It is this interstitialspace into which water is added in order to lubricate the individualparticles so that the hydraulically settable mixture will have adequateworkability and flow properties, particularly when the packing densityis temporarily increased by extruding the mixture under increasedpressure.

b. Water Deficiency.

As stated above, the amount of water which will be added to any givenhydraulically settable mixture should be carefully measured in order toobtain the desired properties of workability and rheology. It will beunderstood, however, that the amount of water to be added to any givenmixture will often have less to do with the volume, or even the mass, ofthe dry hydraulically settable mixture but directly corresponds to thepacking density, more particularly the amount of interstitial voidswithin the mixture.

To better illustrate this point, reference is made to FIGS. 3A and 3B,which show two different particle packing systems having the sameoverall volume and which are both 0% deficient in water. That is, justenough water has been added to completely fill the interstices betweenthe particles. Both of these mixtures will have similar rheologies eventhough they have quite varying amounts of water. As shown graphically inFIGS. 3A and 3B, the mixture having a packing density of 65% (FIG. 3A)has seven times the interstitial water of the mixture having 95% packingdensity (FIG. 3B). (Of course, it would also be predicted that themixture with the higher packing density will have greater strength whencured, according to the Strength Equation.)

FIG. 4 shows an optimized particle packing system in which there is a50% deficiency of water, that is, only half of the interstitial spacehas been filled with water (50% of the space, or 15% of the overallmixture by volume). As a matter of comparison, two hydraulicallysettable mixtures which have the same overall volume and the same volumeof added water will have differing levels of water deficiency whenevertheir particle packing density differs. The lower the packing densitythe greater the water deficiency since there is more interstitial spaceto be filled.

FIG. 5 shows both pictorially and graphically how the application ofpressure to a hydraulically settable mixture, such as by an extruder,causes the particles of the mixture to become more compacted, therebyincreasing their packing density. Because the particles and water areessentially incompressible, the amount of interstitial voids greatlydecreases, while the amount of water available to lubricate theparticles apparently increases. Although air is extremely compressibleand would not significantly impede the compaction process describedabove, it is advantageous to remove the air by means of a vacuum inorder to prevent re-expansion of the air upon release of the compressiveforce.

Knowing just how much water should be added to any given hydraulicallysettable mixture must be carefully calculated prior to actually addingthe water and also verified once the water is added. As stated above,the hydraulically settable binder does not necessarily react with all ofthe theoretical stoichiometric water necessary to hydrate the binder.Instead, some of this water actually fills the interstitial space, atleast temporarily, until it reacts with the hydraulically settablebinder over time.

Of course, it should be understood that the level of water deficiency isnot the only determinant of the rheology of the hydraulically settablemixture. Other additives, such as dispersants and rheology-modifyingagents, greatly affect the viscosity, workability, and other rheologicalproperties of the mixture. One skilled in the art will be able to adjustthe level of water deficiency based on the amount of dispersant and/orrheology-modifying agent that has been added to the mixture to obtain ahydraulically settable mixture having the desired properties.

D. Preparing The Hydraulically Settable Mixture.

As set forth above, any mixing means that is appropriate for aparticular manufacturing process will work well to achieve good particlepacking, although it is believed that the best particle packing densityis achieved by mixing together the aggregates and the hydraulicallysettable binder particles before any water has been added. Once thedesired amount of water is ready to be added, any appropriate mixingprocess may be used. A means for applying high shear to a hydraulicallysettable mixture, such as the high shear mixers described more fullyhereinafter, may be used to create a very homogeneous mixture. Akneader-mixer, such as a clay kneader, is often preferable where lowershear is desired. Finally, the materials may be mixed together andextruded using either a single or twin auger extruder. High frequencyvibration may be used in conjunction with any mixing process to aid inthe mixing of the components.

The currently preferred embodiment for preparing an appropriate moldablemixture in an industrial setting includes equipment in which thematerials incorporated into the moldable mixture are automatically andcontinuously metered, mixed (or kneaded), de-aired, and extruded by anauger extruder apparatus. It is also possible to premix some of thecomponents in a vessel, as needed, and pump the premixed components intoa kneading mixing apparatus.

A double shaft sigma blade kneading mixer with an auger for extrusion isthe preferred type of mixer. The mixer may be adjusted to have differentRPMs and, therefore, different shear for different components.Typically, the moldable mixtures will be mixed for a maximum of about 60minutes, and thereafter emptied from the mixer by extrusion.

In certain circumstances it may be desirable to mix some of thecomponents together in a high shear mixture in order to form a more welldispersed, homogeneous mixture. For example, certain fibers may requiresuch mixing in order to fully disagglomerate or break apart from eachother. High shear mixing results in a more uniformly blended mixture,which improves the consistency of the unhardened moldable mixture aswell as increasing the strength of the final hardened sheet. This isbecause high shear mixing more uniformly disperses the fiber, aggregateparticles, and binder throughout the mixture, thereby creating a morehomogeneous structural matrix within the hardened sheets.

High shear mixers useful in creating the more homogeneous mixtures asdescribed herein are disclosed and claimed in U.S. Pat. No. 4,225,247entitled "Mixing and Agitating Device"; U.S. Pat. No. 4,552,463 entitled"Method and Apparatus for Producing a Colloidal Mixture"; U.S. Pat. No.4,889,428 entitled "Rotary Mill"; U.S. Pat. No. 4,944,595 entitled"Apparatus for Producing Cement Building Materials"; and U.S. Pat. No.5,061,319 entitled "Process for Producing Cement Building Material". Forpurposes of disclosure, the foregoing patents are incorporated herein byspecific reference. High shear mixers within the scope of these patentsare available from E. Khashoggi Industries of Santa Barbara, Calif., theAssignee of the present invention.

Different mixers are capable of imparting differing shear to themoldable mixer. For example, a kneader imparts higher shear compared toa normal cement mixer, but is low compared to an Eirich Intensive Mixeror a twin auger food extruder.

It should be understood, however, that high shear, high speed mixing isgenerally efficacious only where the mixture has relatively lowviscosity. In those cases where it is desirable to obtain a morecohesive, plastic-like mixture, it may be desirable to blend some of theingredients, including water, in the high shear mixer and thereafterincrease the concentration of solids, such as fibers or aggregates,using a lower shear kneading mixer.

In many cases the order of mixing will impart different properties tothe hydraulically settable mixture. In a currently preferred embodimentin which both a dispersant and a rheology-modifying agent are used, itwill be preferable to first mix the hydraulically settable binder andwater together using a high shear mixer. The dispersant is preferablyadded after significant wetting of the hydraulically settable binderparticles has occurred. After the dispersant has been substantiallyadsorbed by the hydraulically settable binder particles, therheology-modifying agent is added to the mixture.

E. Extruding Articles From The Hydraulically Settable Mixture.

Once the moldable mixture has been properly blended, it is thentransported to an extruding means such as an auger extruder, a pistonextruder or a twin auger extruder and extruded. Although thehydraulically settable mix designs of the present invention havecarefully controlled theology and plastic-like properties which makethem suitable for other molding processes, the essential feature of theproducts of the present invention is that they can be continuouslyextruded. It is this continuous extrusion process which allows theformation of a wide variety of objects and shapes in an economical andinexpensive fashion.

As stated above, a combination of particle packing density, waterdeficiency, and compression during the extrusion process creates ahydraulically settable mixture with discontinuous theologicalproperties. Hence, an important criterion in any extrusion process ischoosing an extruder which is capable of exerting a carefullypredetermined pressure for any given mix design. This is because thecompressive forces of the extruder are responsible for temporarilyincreasing the particle packing density, which decreases the volume ofinterstitial space and decreases the effective water deficiency of themixture. This immediately translates into better lubricated particlesand increased workability and flow properties.

However, the best properties are generally obtained by exerting apressure which is commensurate with the levels of particle packing,water deficiency and aggregate strength within the mixture. Adding toolittle pressure would prevent the ability to impart adequate flowproperties to the hydraulically settable mixture. Conversely, adding toomuch pressure might also cause a number of problems, including thepulverization of certain aggregates within the hydraulically settablemixture, a tendency of the extruded material to burst out of theextruder die rather than continuously flowing out, or non-uniformity offlow through the die.

Depending on the amount of pressure that is desired and the amount oftype of shear to be exerted onto the hydraulically settable mixture,either a piston-type or auger-type extruder can be used. An auger-typeextruder (FIG. 6) has certain advantages even though it cannot be usedto extrude at the same high pressures as a piston extruder. Theseadvantages include continuous internal shear which is applied by theturning auger screw, as well as greater ease in continuously applying avacuum or negative pressure to the hydraulically settable mixture withinthe auger extruder to remove any unwanted air within the mixture. Insome cases, an apparatus capable of both mixing and extruding themoldable mixture may be used in order to streamline the operation andminimize the coordination of the various components within the system.The advantage of the piston-type extruder as shown in FIG. 7 is thegreater amount of pressure which can be applied. In order to apply veryhigh pressures, even up to 100,000 psi, the only currently knownpossibility is to use a piston extruder or a roller milling/extrudingprocess. The piston of a piston extruder and the auger of an augerextruder are merely examples of means for applying an extrusion pressuresufficient to cause a hydraulically settable mixture to flow and beextruded through a die; other means can also be utilized.

Reference is now made to FIG. 6, which is a closeup view of an augerextruder 20, which includes a feeder 22 that feeds the moldable mixtureinto a first interior chamber 24 within the extruder 20. Within thefirst interior chamber 24 is a first auger screw 26 which exerts forwardpressure on and advances the moldable mixture through the first interiorchamber 24 toward an evacuation chamber 28. Typically, a negativepressure or vacuum will be applied to the evacuation chamber 28 in orderto remove unwanted air voids within the moldable mixture.

Thereafter, the moldable mixture will be fed into a second interiorchamber 30. A second auger screw 32 will advance the mixture toward adie head 34 having a transverse slit 36 with a die width 38 and a diethickness 39. The cross-sectional shape of the die slit 36 is configuredto create a sheet of a desired width and thickness that will generallycorrespond to the die width 38 and die thickness 39.

Alternatively, as seen in FIG. 7, the extruder may comprise a pistonextruder 20' instead of an auger extruder 20. A piston extruder utilizesa piston 22' instead of an auger screw 22 in order to exert forwardpressure on and advance the moldable mixture through the interiorchamber 24'. An advantage of using a piston extruder is the ability toexert much greater pressures upon the moldable mixture. Nevertheless,due to the highly plastic-like nature of mixtures typically employed inthe present invention, it is not generally necessary, or evenadvantageous, to exert pressures greater than those achieved using anauger extruder.

A currently preferred system for large scale mixing and extrusion in anindustrial setting involves equipment in which the materialsincorporated into the hydraulically settable mixture are automaticallyand continuously metered, mixed, de-aired, and extruded by a twin augerextruder apparatus. A twin auger extruder apparatus has sections withspecific purposes such as low shear mixing, high shear mixing,vacuuming, and pumping. A twin auger extruder apparatus has differentflight pitches and orientations which permits the sections to accomplishtheir specific purposes.

It is also possible to premix some of the components in a vessel, asneeded, and pump the premixed components into the twin auger extruderapparatus. The preferable twin auger extruder apparatus utilizes uniformrotational augers, wherein the augers rotate in the same direction.Counter-rotational twin auger extruders, wherein the augers rotate inthe opposite directions, accomplish the same purposes. A pug mill mayalso be utilized for the same purposes. Equipment meeting thesespecifications are available from Buhler-Miag, Inc., located inMinneapolis, Minn.

The amount of pressure that is applied in order to extrude the moldablemixture will generally depend on the pressure needed to force themixture through the die head, as well as the desired rate of extrusion.The rate of extrusion should be carefully controlled in somecircumstances in order for the rate of formation of the extruded articleto correspond to the rate of subsequent processing steps, such ascutting and/or reformation of the extruded article. An important factorwhich will affect the optimum speed or rate of extrusion is the finalthickness of the extruded article. A thicker article contains morematerial and will require a higher rate of extrusion to provide thenecessary material. Conversely, a thinner article contains less materialand will require a lower rate of extrusion in order to provide thenecessary material.

The ability of the moldable mixture to be extruded through a die head,as well as the rate at which it is extruded, is generally a function ofthe rheology of the mixture, as well as the operating parameters andproperties of the machinery. Factors such as the amount of water,hydraulically settable binder, rheology-modifying agent, dispersant, theparticle packing density, or the level of water absorption or reactionby the mixture components all affect the rheological properties of themixture.

As set forth above, adequate pressure is necessary in order totemporarily increase the workability of the moldable mixture in the casewhere the mixture has a deficiency of water and has a degree of particlepacking optimization. In a mixture that is water deficient, the spaces(or interstices) between the particles contain insufficient water tolubricate the particles in order to create adequate workability underordinary conditions. However, as the mixture is compressed within theextruder, the compressive forces drive the particles together, therebyreducing the interstitial space between the particles and increasing theapparent amount of water that is available to lubricate the particles.In this way, workability is increased until the mixture has beenextruded through the die head, at which point the reduced pressurecauses that mixture to exhibit an almost immediate increase in stiffnessand green strength, which is generally desirable.

In light of each of the factors listed above, the amount of pressurewhich will be applied by the extruder in order to extrude the moldablemixture will preferably be in a range from about 10 bars to about 7000bars, more preferably in a range from about 20 bars to about 3000 bars,and most preferably in a range from about 50 bars to about 200 bars.

It will be understood that the extrusion of the moldable mixture throughthe die head will tend to unidirectionally orient the individual fiberswithin the moldable mixture along the "Y" axis, or in the lengthwisedirection of the extruded article.

As set forth above, it may also be desirable to co-extrude thehydraulically settable mixture with other materials in order to obtain,e.g., a laminate structure or an extruded product with other materialsimpregnated within the hydraulically settable matrix. Things which maybe co-extruded with the extrudable hydraulically settable mixtures ofthe present invention include another hydraulically settable mixture(often having different or complementary properties), a fibrous mat,coating materials, polymers, clays, graphite (for making a pencil), orcontinuous fibers, strips, wires, or sheets of almost any other material(such as metal). It has been found that by joining together, forexample, a hydraulically settable sheet and a fibrous mat byco-extrusion that the final product exhibits synergistic results ofstrength, toughness, and other performance criteria.

F. Accelerated Drying.

Although the hydraulically settable materials of the present inventionare capable of quickly gaining high green strength, it may yet bedesirable to accelerate further the hardening or stiffening of theextruded materials. This can be accomplished by applying heat to furtherremove some of the water within the hydraulically settable mixture,particularly from the surface, where the greatest amount of greenstrength is often desired. Heating is especially desirable where thereis an excess of water within the mixture in order to increase theviscosity and yield stress of the extruded article and impart thedesired rapid form-stability.

Because of the nature of extrusion, it will usually not be advantageousto overheat the extruder die above a certain temperature in order toremove water during the extrusion process. Overheating the die mightcause the extruded mixture to expand or form pockets of high pressuresteam that can cause the hydraulically settable mixture to "explode" outof the extruder die. (Nevertheless, some degree of heating may bedesirable in order to reduce the friction between the extruded materialand the extruder die by forming a steam barrier.) By careful control ofthe rheology of the hydraulically settable mixture and appropriateheating of the extruder die, it is generally possible to obtain extrudedarticles having strength to allow handling immediately after extrusion.

G. Accelerated Curing.

In those cases in which the extruded hydraulically settable mixture isso water deficient that there is insufficient water to adequatelyhydrate the cement or other hydraulically settable binder, it might beadvantageous to expose the extruded object to water or air having highhumidity. The hygroscopic nature of typical binders, particularlyhydraulic cement, allows the binder to literally absorb the necessarywater of hydralion from the air. Although this would occur naturally inany event (at least in the case of hydraulic cement), exposing the verywater deficient extruded object to air having high humidity greatlyincreases this water absorption process and the rate of hydration of thebinder particles. In particular, autoclaving may be used in order togreatly increase the strength of the final cured article.

III. PLACING FILAMENTS DURING EXTRUSION.

The present invention provides apparatus and methods for continuouslyextruding a hydraulically settable mixture and simultaneously placingfilaments within the mixture to form novel articles of manufacturehaving a filament reinforced hydraulically settable structural matrix.The primary purpose of incorporating continuous filaments is to increasethe modulus of elasticity, elongation modulus, tensile strength,flexural strength, toughness, and peak load before rupture of anarticle. The circumferential, bursting or hoop strength of an articlecan also be increased by increasing the angle α of the filaments, whichstrength is essential in the functionality of pipes, containers, and allother pressure vessels, particularly thin-walled pressure vessels(containers whose wall thickness to radius ratio is less than 0.1). Thefilaments can be placed anywhere within the hydraulically settablestructural matrix, including in the interior and/or on the surface ofthe structural matrix.

Filaments can be placed in any desired orientation within thehydraulically settable structural matrix by introducing filaments intothe die of an extruder as a hydraulically settable mixture is beingextruded. This action causes the filaments to be "drawn" into theextruding hydraulically settable mixture. The hydraulically settablemixture encapsulates the filaments and becomes consolidated or compactedas a result of the internal pressure applied to the mixture during theextrusion process, thereby minimizing the amount and volume of internalvoids or defects within the mixture and maximizing the interface betweenthe filaments and the hydraulically settable mixture. Increasing theinterface between the filaments and the matrix helps to more securelyanchor the filaments within the hydraulically settable matrix.

Different embodiments of the apparatus for continuously placingfilaments within the extruding hydraulically settable mixture permit thefilaments to be placed in a variety of configurations or orientations.These include a parallel configuration, helical configuration,criss-cross configuration, or combinations of these configurations. In a"parallel configuration" the filaments are generally coaxial to thelongitudinal axis, or extrusion direction, of the hydraulically settablearticle. Conversely, in the "helical configuration" and "criss-crossconfiguration" (which is merely a variation of the helicalconfiguration), the filaments are offset from the longitudinal axis,usually at an angle α of at least about 5° up to a maximum of about 90°,which may be referred to herein as the "offset angle", "winding angle"or "spiral angle". (Depending on the direction of rotation of thefilament placing means, i.e., clockwise or counterclockwise, angle α caneither be positive or negative but will not have a magnitude greaterthan 90°, an angle of 91° being identical to an angle of -89°.)

The placement of filaments within the hydraulically settable mixturewithout any significant winding or similar movement of the filamentswhile the filaments are being introduced into the interior chamber ofthe extruder die yields a parallel, coaxial configuration of filamentswithin the extruded article. Winding the filaments upon introducing thefilaments into the extruder die produces an article having a spiralconfiguration of filaments within the hydraulically settable structuralmatrix. A criss-cross configuration is achieved by winding filaments inthe opposite direction relative to the direction of previously woundfilaments. Specifically, winding one filament clockwise and anotherfilament counter clockwise yields overlapping fibers in a criss-crossorientation, one filament having a positive angle relative to thelongitudinal axis and the other filament having a negative anglerelative to the longitudinal axis.

The concentration or volume of filaments relative to a given volume ofthe hydraulically settable matrix of the extruded article isproportional to the number, cross-sectional area, and the magnitude ofthe winding angle α of the filaments. Increasing any or all of thesevariables will increase the concentration or volume of the filamentswithin the hydraulically settable matrix. In particular, increasing themagnitude of the winding angle α increases the frequency of eachindividual winding, which simultaneously decreases the distance betweeneach winding, thereby increasing the concentration (and, hence, volume)of filament per unit length of the extruded article.

By varying the concentration and/or the winding angle α of the filamentsplaced within the extruded hydraulically settable articles of thepresent invention, a wide variety of strength, elongation, and toughnessproperties can be attained. Additionally, depending on their chemicalmakeup, the filaments themselves can have greatly varying tensile andshear strengths, as well as flexibility and elongation ability. Suchproperties are also affected by the diameter of the filaments, orwhether the filaments consist of a single strand or a group of strandstwisted or otherwise joined together to form a single filament unit.

A primary factor affecting the properties imparted to the final hardenedarticle by the wound filaments is the offset angle. Some of theproperties affected by the offset angle include the hoop strength,tensile strength, and flexibility of the article. The preferred offsetangle depends on many factors, including the shape of the article beingextruded, the type of filament, the desired strength properties of thearticle, and cost. Filaments having a lower winding angle will generallydefine an elliptical cross section of the pipe or cylinder into whichthey are placed. As the winding angle increases to 90°, the filamentswill tend to define an ellipse of diminishing cross-width. At an angleof 90°, the filaments will define a circular cross section.

Assuming that the article being extruded is a pipe, cylinder, or otherarticle having a generally circular cross-section, it will have a radiusthat is generally perpendicular to the longitudinal axis. For purposesof defining the direction and magnitude of the strength imparted by thefilaments, it would be useful to define the strength imparted by thefilaments as having vector components corresponding to the longitudinalaxis and radius, respectively. Whenever a filament has an angle ofoffset greater than 0° but less than 90°, the filament will have both alongitudinal vector component and a radial vector component. Infilaments having a winding angle less than 45°, the longitudinalstrength vector would be expected to generally exceed the radialstrength vector. Similarly, in filaments having a winding angle greaterthan 45°, the radial strength vector would be expected to generallyexceed the longitudinal strength vector.

In general, more longitudinally oriented filaments having a greaterlongitudinal strength vector will tend to increase the tensile strengthof the hydraulically settable article in the longitudinal, or lengthwisedirection. Conversely, filaments having a greater angle of offsetrelative to the longitudinal axis, i.e., those having a greater radialstrength vector will instead tend to increase the circumferentialstrength (otherwise known as hoop or burst strength in the case of apipe or other hollow structure). A mixture of filaments having bothhigher and lower angles of offset can be used in order to impart each ofthese properties.

The angle α at which the filament is placed is a function of both theforward extrusion speed ("V_(e) "), as well as the rotational velocity("V_(r) ") of the placing means. In fact, the tangent of angle α isproportional to the ratio of the rotational velocity to the extrusionspeed (V_(r) /V_(e)). Therefore, all things being equal, the faster theextrusion speed, the lower the angle of offset of the filaments.Conversely, the greater the magnitude of the rotational velocity of theplacing means the greater the magnitude of the winding angle of thefilaments. The concentration of filaments within the hydraulicallysettable matrix of the extruded article is directly proportional to boththe number of filaments, as well as the average angle α of thefilaments. As both the number and average angle α of the filamentsincreases, so does the concentration. The greater the concentration offilaments, the less space there is between the individual filamentstrands. This results in a greater and more uniform effect imparted bythe filaments to the hydraulically settable matrix of the extrudedarticle. In general, smaller diameter fibers more closely spacedtogether will tend to more uniformly impart the desired properties of,e.g., strength, flexibility, and toughness compared to larger diameterfibers.

Finally, the relative placement depth of the various individualfilaments affects the spacial orientation of the filaments, which, likeconcentration and winding angle, can affect the strength, flexibility,and other properties of the final hardened article. More evendistribution of the placement depth of the individual filaments yields afinal product with more uniformly distributed filaments, which betterdistributes any load or impact that is applied to the extruded article.

In most cases, it will generally be preferable to place the filaments ina manner which achieves uniform strength throughout the article.Nevertheless, the particular performance criteria of any given articlewill dictate the optimal placement of filaments therein. The filamentscan be initially placed at an optimal depth or the filaments can befurther positioned within the hydraulically settable structural matrixby pulling the filaments deeper into the mixture after being initiallyplaced. A number of independent factors work together in affecting thedepth of fiber placement, including tension of the filaments, theviscosity of the mixture, the extrusion rate of the mixture, and therotational rate of the placing means.

Filaments are drawn from the placing means by the mixture primarily dueto the frictional force between the mixture and the filaments, which iscontrolled, at least in part, by controlling the viscosity of themixture. As previously discussed, however, to increase the workabilityof the hydraulically settable mixture so as to enable extrusion of themixture at a minimum cost, it is preferable to lower the viscosity ofthe mixture while maintaining an adequate yield stress to maintain formstability. In the preferred embodiment, these opposing conditions areoptimized. Too high a viscosity can waste energy or prevent extrusion ofthe mixture or cause the filament to break, while too low of a viscositycan cause the filament to slip within the mixture and thus preventuniform alignment of the filament. As previously discussed, viscosity ofthe mixture can be varied by numerous methods such as altering thepacking density, increasing the water content, or the addition ofadmixtures such as dispersants or water reducers.

Filaments can be placed deeper within a hydraulically settablestructural matrix after being initially drawn from the placing means bymaintaining an optional tension on the filaments as the filaments arewound. Tension on the filaments causes the filaments to be pulled intothe hydraulically settable structural matrix by the rotation on theplacing means.

The amount of penetration of the filament within the extruded article isinversely proportional to the length of filament laid down during anygiven rotation distance, as the are defined by the circumference of theextruded article has a greater length than a chord defined by two pointsalong the arc. The length, in turn, is inversely proportional to thetension on the filament. In other words, by increasing the tension onthe filament being wound, the length of filament being laid down duringthe rotation of the rotatable placing means decreases. This, in turncauses the filament to be pulled down within the extruded material. Byadjusting the tension of the filament, as well as the rotationalvelocity and extrusion rate, one skilled in the art can control thedepth of the filament penetration within the extruded material.

Depicted in FIGS. 8-29 are filaments being placed within a hydraulicallysettable mixture by an apparatus comprising means for continuouslyplacing filaments within a hydraulically settable composition beingextruded into a desired article. The filaments are shown in FIGS. 8-21being introduced into a die or interior chamber of an extruder of thepresent invention; the interior chamber is herein referred to as a"filament placement chamber", an "interior die chamber", or simply"die". A specific embodiment of an apparatus for continuously placingfilaments in a hydraulically settable composition is shown in FIGS.22-29.

The methods and apparatus described below can also be used withmaterials other than hydraulically settable mixtures. By way of exampleonly, other materials which can be utilized with the methods andapparatus of the present invention include plastics, clays, mixtures ofclay and fibers, or mixtures comprising an organic binder and inorganicaggregates as described in co-pending U.S. patent application Ser. No.08/218,971, entitled "Methods Of Molding Articles Having AnInorganically Filled Organic Polymer Matrix," and filed Mar. 25, 1994,in the names of Per Just Andersen, Ph.D., and Simon K. Hodson, which isincorporated herein by specific reference. Similarly, the presentinvention can be utilized with mixtures comprising an organic binder andorganic aggregates.

FIGS. 8-10 depict filaments being introduced into a die of an extruder,placed within a hydraulically settable mixture, and wound into a spiralconfiguration. Depicted in FIG. 8 is a longitudinal cross-section viewof the apparatus shown generally at 50 for placing filaments duringextrusion of a hydraulically settable mixture shown at 52. Thehydraulically settable mixture 52 is extruded within a filamentplacement chamber 54 in the direction indicated by arrow 56 toward meansfor placing filament. The placing means are disposed around andcommunicate with filament placement chamber 54, with each placing meanscomprising means for receiving filament into the placing means, meansfor channeling the received filament through the placing means andintroducer means for introducing filaments into the filament placementchamber, after which the filaments are drawn by the internal friction orviscosity of the hydraulically settable mixture.

In the embodiment of the apparatus shown in FIG. 8, the means forreceiving a filament into the placing means comprises a filament entry58; the means for channeling the received filament through the placingmeans comprises a channel 60; and the means for introducing the filamentinto the interior die chamber comprises scoop end 62. Inserted througheach filament entry 58 is a filament 64 that extends through channel 60and is introduced by scoop end 62 into filament placement chamber 54. Aportion of filament placement chamber 54 is shown in FIG. 8 with acircular cross-section; however, filament placement chamber 54 can haveany cross-section, length, or shape necessary to manufacture a desiredarticle.

FIG. 8 shows filament placement chamber 54 tapering to have anincreasingly smaller diameter towards the exit end of filament placementchamber to provide means for maintaining back pressure on the system.Back pressure assists in maintaining constant pressure within thefilament placement chamber or die, which improves the compaction of thehydraulically settable mixture and the resulting interface between thehydraulically settable matrix and the filaments. Compaction of thehydraulically settable mixture around the filaments results in betterencapsulation of the filaments, increased uniformity, and fewer voidswithin the mixture, which collectively optimize the interface betweenthe filaments and the hydraulically settable mixture and help tosecurely anchor the filaments within the hardened article. The backpressure within filament placement chamber 54 effectively fills anygrooves or perforations created by the penetrating filaments as theyenter and cut through the hydraulically settable structural matrixduring placement, usually by wound filaments. It is particularlydesirable to provide adequate back pressure when filament placementchamber 54 is long and when large amounts of filaments are incorporatedinto the hydraulically settable structural matrix.

The placing means shown in FIGS. 8-10 are rotatable to provide means forwinding filaments into a helical or spiral configuration within thehydraulically settable matrix as the hydraulically settable mixture isextruded. A means for rotating the placing means (not shown in FIGS.8-11 ) rotates the placing means around filament placement chamber 54.The placing means can also remain stationary or in a fixed position toyield filaments of a generally parallel configuration extending alongthe same axis as the extrusion direction. The placing means can have anyshape necessary to place non-cylindrical or odd-shaped filaments, suchas rovings or mats.

As the mixture is extruded, it passes around scoop ends 62 (as depictedin the longitudinal cross-section of FIG. 9), encapsulates the filamentsextending from scoop ends 62, and pulls the filaments in the extrusiondirection 56. The filaments are pulled from the scoop ends 62 due to theinternal friction or viscosity of the hydraulically settable mixture.Upon curing of the hydraulically settable mixture, the filaments aresecurely incorporated within the hydraulically settable matrix, therebyproviding the aforementioned reinforcement and strength properties. Thefilaments and the hydraulically settable mixture together form acontinuous article 66 or extrudate of any desired length. The extrudatecan also be cut into smaller articles of any desired length, therebypermitting continuous production of even relatively small articles. Byway of example only, article 66 being formed in FIG. 9 is a rod or abar.

The design of the placing means assists in determining the configurationof the filaments within the mixture and the placement depth of thefilaments within the hydraulically settable matrix. Depicted in FIG. 10is a transverse cross-section view taken along cutting plane line 10--10of FIG. 9 depicting scoop ends 62 extending into filament placementchamber 54 and the perimeter 68 of article 66 after it is extruded. Theplacement depth is determined, at least in part, by the length of theportion of the placing means that extends into filament placementchamber 54. Placement depth is also increased by increasing the tensionof the filament.

The angle of the placing means, which directly corresponds to the exitangle of the filament (i.e., the angle in which the filament exits theplacing means), can also affect the strain on the filament as it iswound into the hydraulically settable mixture. In general, strain on thefilaments is minimized by minimizing the difference between the windingangle and the exit angle of the filament. The difference is minimized bydesigning the placing means to yield an exit angle which issubstantially the same as the winding angle. Increasing the differencebetween the exit angle and winding angle of the filament tends toincrease the friction between the filament and the placing means,thereby creating more tension on the filament being placed. As statedabove, increasing the tension of the filament will generally increasethe placement depth of the filament, often in an unwanted fashion.

As discussed above, the placing means shown in FIGS. 8-10 can alsoremain fixed, as shown in FIG. 11, which depicts a longitudinalcross-section view of an apparatus to yield filaments in a parallelconfiguration extending along the longitudinal axis of the filamentplacement chamber 54. Other embodiments of the placing means are shownin FIGS. 12, 13 and 14, which can also be rotated or remain stationary.FIG. 12 is a longitudinal cross-section view of the apparatus having aplacing means comprising a filament entry 70, a channel 72, and anintroducer comprising a nib end 74. The placing means in FIG. 12 remainsstationary to form a parallel configuration of filaments within thehydraulically settable matrix. Depicted in FIG. 13 is a transversecross-section view of the placing means and filament placement chamber54 shown in FIG. 12 taken along cutting plane 13--13 of FIG. 12, whichdepicts nib ends 74 extending into filament placement chamber 54 and theshape of the article after it is extruded.

FIG. 14 illustrates a longitudinal cross-section view of anotherembodiment of the placing means. Each placing means in FIG. 14 comprisesa filament entry 76, a channel 78, and an introducer comprising a hollowneedle 80. The placing means shown in FIG. 14 can be incrementallypositioned deeper into filament placement chamber 54 to help vary theplacement depth of the filaments within the hydraulically settablestructural matrix. The placing means embodied in FIGS. 8-14 areillustrative and not restrictive and may be embodied in any otherstructure or structures capable of placing filaments within thehydraulically settable structural matrix.

The strength of the article being formed can be further increased byplacing more filaments into the mixture by one or more additional setsof placing means that are offset from the first set of placing means.For example, a second filament can be placed closer to the surface ofthe matrix compared to a previously placed filament. Additionally,multiple sets of placing means which are rotatable or fixed can be usedin combination to place filaments into a variety of combinations orconfigurations. For example, filaments can be wound into a hydraulicallysettable mixture in the opposite direction of filaments which have beenpreviously wound.

Depicted in FIG. 15 is a longitudinal cross-section view of apparatus 50extruding the hydraulically settable mixture 52 in the extrusiondirection indicated by arrow 56, while simultaneously placing filaments64 in a "criss-cross" configuration within the hydraulically settablemixture 52. Two sets of rotating placing means comprising filament entry70, channel 72, and nib end 74 rotate in opposite directions to windfilaments within the structural matrix in opposite directions, resultingin a criss-cross configuration of filaments.

Depicted in FIG. 16 is a longitudinal cross-section view of apparatus 50extruding the hydraulically settable mixture 52 in the extrusiondirection 56, while simultaneously placing filaments 64 in a parallelconfiguration and a criss-cross configuration within the hydraulicallysettable mixture 52. In the extrusion direction 56, filaments are firstplaced by fixed placing means comprising filament entry 70, channel 72,and nib ends 74 in a parallel configuration. Filaments are placed overthe parallel filaments in a criss-cross configuration by two sets ofrotating placing means, which also comprise filament entry 70, channel72, and nib ends 74, and which rotate in opposite directions to wind thefilaments within the hydraulically settable mixture in oppositedirections.

Although typically the greater the absolute strength of the filamentsthe fewer the filaments that will be needed, the filaments arepreferably sufficiently dispersed throughout the article to distributethe desired strength properties throughout the entire article. Oneskilled in the art of materials science will be able to determine inadvance, or through minimal testing based on the teachings herein, theactual size, strength, number, and orientation of the filaments thatshould be placed within the hydraulically settable matrix in order toobtain the desired properties.

It may also be desirable to place different types of filaments withinthe same article. Additionally, other materials can be coextruded withthe hydraulically settable mixture and filaments. The hydraulicallysettable mixture and filaments can be coextruded around a material or amaterial can be coextruded around the mixture and the filaments. Themixture and the filaments can, for example, be coextruded around lead toform pencils or a coating can be coextruded around the mixture and thefilaments.

One of the primary benefits of the methods and apparatus of the presentinvention is the ability to form articles having a variety of shapeswith any type and quantity of filament selectively positioned within thearticles. The shape of the article is determined primarily by the shapeof the filament placement chamber 54 and any mandrels included withinfilament placement chamber 54 for introducing a cavity or hollow spacewithin the extruded article. The configuration or spatial orientation ofthe filaments placed within the hydraulically settable structural matrixdepends on the design of the placing means, including the depth at whichthe filaments are introduced, as well as the speed at which the placingmeans are rotated.

In designing a desired article, the filament is selected and thefilament configuration is determined based primarily on the stresses towhich the article will be subjected. For example, an I-beam that will besubject to transverse loading would preferably have filaments positionedat a distance from the centroidal axis in the portion of the membersubject to tension, thereby increasing the flexibility of the beam andthe peak load to failure. FIG. 17 depicts a perspective view ofapparatus 50 having placing means located around an I-shaped filamentplacement chamber 54, which is shown in a cut-away view. Apparatus 50 inFIG. 17 is shown forming an article 66 shaped as a continuous I-beam.The continuous extrudate or article can be cut into an individual I-beamby a means for cutting the extrudate. The cutting means can comprise aspinning blade 82, a fixed blade such as a guillotine, a saw, or anyother structure capable of cutting through the hydraulically settablestructural matrix and filaments therein.

Articles, such as boards, "two-by-fours", plywood, counter tops,corrugated structures, flat sheets, and roofing tiles can be formed byextruding a hydraulically settable mixture and placing filaments in aparallel configuration within the matrix. FIG. 18 is a perspective viewof apparatus 50 with a slit-shaped filament placement chamber 54 andfixed placing means located around filament placement chamber 54, whichillustrates the formation of a flat hydraulically settable sheet 66 withfilaments in a parallel configuration.

Filaments can also be placed in a helical configuration withinhydraulically settable articles that do not have a circularcross-section, such as boards. As depicted in the perspective view ofapparatus 50 in FIG. 19, an article can be formed with a non-circularcross-section, yet have a matrix with a helical configuration offilaments. Apparatus 50 in FIG. 19 has a filament placement chamber 54shown in a cut-away view having a circular cross-section throughout itslength until it reaches or extends to the "exit end" or "exit die" whichhas a different cross-section in the shape of the desired article. Thecorners and the perimeter of the article can be reinforced with parallelfilaments. Such articles can also be made by designing filamentplacement chamber 54 with a circular cross-section in the area of therotatable placing means, which gradually transcends in the extrusiondirection into a non-circular cross-section at the exit die.

A mandrel can also be positioned within filament placement chamber 54 toform tube-like articles with a hollow cross-section, such as pipes ortubes. The mandrel can have any shape and any cross-section as long asthe mixture can be extruded around it. It may be desirable for themandrel to be tapered, having a smaller diameter at the beginning of thefilament placement chamber than at the end. The tapered mandrel enhancesthe ability of the system to maintain back pressure, which assists incompacting the mixture and increases the interface between the mixtureand filaments.

Mandrels are also useful in forming tubular articles having anon-circular cross-section, such as rectangular tubes, with a structuralmatrix containing a helical configuration of filaments. As depicted inthe perspective view of apparatus 50 in FIG. 20, such articles can bemade by utilizing a filament placement chamber 54 shown in a cut-awayview with a circular cross-section in the area of the rotatable placingmeans which gradually transcends to a non-circular cross-section and amandrel 84, which also makes a similar transition from a circularcross-section to a non-circular cross-section. The mandrel 84 can alsobe designed to have cross-section areas of transitioning shapes alongthe length of the mandrel, the cross-sectional areas having anapproximately equal perimeter, which enhances the shape and strength ofthe helical winding.

Additionally, multiple mandrels can be positioned within the filamentplacement chamber to form multi-chambered articles such as hollowbricks, honeycomb, or other multicellular structures. FIG. 21 depictshollow bricks being formed by an apparatus 50 having three mandrels 84,shown in a cut-away view of filament placement chamber 54, and placingmeans around filament placement chamber 54 having a rectangularcross-section. As with the other extrudates, the continuous "brick" canbe cut into the desired length by cutting means, such as cutter 82, toform individual bricks.

FIGS. 22-29 show another embodiment of apparatus 50 capable of placingfilaments into helical configurations, criss-cross configurations,parallel configurations, or combinations thereof. Filaments can beplaced by apparatus 50, as shown in FIGS. 22-29, during the extrusion ofa hydraulically settable mixture. The simultaneous placement offilaments and extrusion of the hydraulically settable mixtures enablesthe continuous production of articles reinforced with spiral woundfilaments.

FIG. 22 is a perspective view, and FIG. 23 is a side elevational view,showing apparatus 50 having a filament placement chamber 54 in directcommunication with an interior chamber 24' of a piston extruder.Disposed around filament placement chamber 54 are three feeder rings, asshown generally at 100, 102 and 104, comprising means for storing andcontinuously providing filaments 64 to the placing means (not shown inFIGS. 22 and 23), which, in turn, introduces the Filament into filamentplacement chamber 54. A set of fixed placing means are disposed aroundfilament placement chamber 54, which receives filaments from fixedfeeder ring 100. One set of rotatable placing means receives filamentfrom and rotates with rotatable feeder ring 102. Another set ofrotatable placing means receives filaments from rotatable feeder ring104, which rotate together in the opposite direction of the other set ofrotatable placing means.

Each feeder ring comprises a feeder ring frame 106 and at least onefilament dispenser or creel, such as filament spools 108. The filamentdispensers are positioned on feeder rings 100, 102, 104. A filamentdispenser can also be utilized without the feeder rings to comprise ameans for storing and continuously providing filaments to a placingmeans. By way of example and not limitation, a filament dispenser whichcan store and continuously provide filaments without being positioned ona feeder ring is a conventional creel used in conventional filamentwinding methods.

The filament dispenser can either freely rotate on a spindle withouttension, or else a tensioning means for varying filament tension can beutilized to vary the tension of the filaments 64 being dispensed fromthe filament dispensers, such as tensioner 110. Each tensioner 110 inthe embodiment shown in FIG. 22 comprises a hollow spindle (not shown)with inner threads (not shown) to receive a threaded bolt (not shown)with a bolt head 112 capable of engaging the top of filament spool 108.Increasing or decreasing the contact between the top of filament spool108 and bolt head 112, usually by tightening and loosening the threadedbolt, varies the tension of the filament being dispensed. The tensionermay also comprise a spring positioned around the spindle and betweenbolt head 112 and filament spool 108. Another embodiment of thetensioning means includes motorized movement of the spools 108.

Means for rotating the placing means engage the rotatable feeder rings102 and 104, which are rigidly attached to the rotatable placing means,and thereby rotate the rotatable placing means. The embodiment of therotating means shown in FIG. 22 comprises a motor 114, a belt 116, and agroove 118 on each respective rotatable feeder ring for receiving belt116. Each motor 114 moves each belt 116, which in turn rotates therespective rotatable feeder ring. The motors 114 are mounted on asupport frame 120, which is attached to the extruder (not shown). Thesupport frame further supports the apparatus by members 122, which areattached to clamps 124.

Another embodiment of the rotating means comprises a motor which rotatesa sprocket, which in turn engages the links of a chain, which alsoengage teeth located around the feeder ring to thereby rotate therotatable feeder ring. An additional embodiment of the rotating meanscomprises a motor which rotates a sprocket that directly engages teethlocated around the feeder ring to thereby rotate the rotatable feederring. The rotating means may be digitally controlled for improvedaccuracy. The rotating means also includes controls with a feedbackmechanism to monitor and control the rotation rate in relation to theextrusion rate. The rotating means may be embodied in any otherstructures capable of rotating the placing means directly or by rotatinga feeder ring attached to the placing means. The rotating meansdescribed above are, of course, merely illustrative and not restrictive.

The components of apparatus 50 and the path of the hydraulicallysettable mixture through apparatus 50 are best viewed in FIGS. 24 and25. Referring to FIG. 24, which depicts a cross-section view of theapparatus 50 taken along cutting plane line 24--24 of FIG. 22, and toFIG. 25, which depicts an exploded perspective view of the apparatus,filament placement chamber 54 is defined by a bore 130 of an entrancedie 132, a bore 134 of a rotatable channel carriage 136, a bore 138 ofanother rotatable channel carriage 140, and a bore 142 of an exit die144. The hydraulically settable mixture is continuously extruded fromthe interior chamber 24' into bore 130 of entrance die 132 through bores134 and 138 of rotatable channel carriages 136 and 140 and out of bore142 of exit die 144.

The cross-sectional area of filament placement chamber 54 can beconsistent along the entire length of filament placement chamber 54 orit can vary in size and shape. A cross-section of filament placementchamber 54 can have any shape including, without implied limitations, around, square, elliptical, or triangular cross-section. In FIG. 24,filament placement chamber 54 is shown with a circular cross-sectionthroughout the entire length of the filament placement chamber and aslightly decreasing diameter in the extrusion direction. Thehydraulically settable mixture is extruded through one bore and into abore having a smaller diameter than the previous bore to furthercompress the mixture and position the filament within the hydraulicallysettable structural matrix. As previously discussed, it is generallydesirable for the cross-sectional area of the filament placement chamberto become increasingly smaller towards the exit end or die to maintainback pressure on the system, which assists in filling in the groovescreated by the placement of filaments within the hydraulically settablestructural matrix.

As shown at 84 in FIG. 24, the filament placement chamber can also beconfigured with a mandrel to form tubular articles, such as pipes. Themandrel can be untapered or tapered, as shown in FIG. 24, to assist inmaintaining back pressure on the system and can be utilized with afilament placement chamber, which can be either tapered or untapered asexplained above. When utilizing a mandrel with piston extruder 20, it isnecessary to attach the mandrel to extruder 20 with a spider 150 locatedbetween mandrel 84 and extruder 20. Spider 150 has tapered legs 152radiating from the center to the perimeter, which allow thehydraulically settable mixture to flow around legs 152 and then comeback together after passing around legs 152. Spider 152 is not necessarywhen apparatus 50 is attached to an auger extruder.

To achieve a parallel configuration of filaments within thehydraulically settable matrix, filaments are delivered from spools 108on fixed feeder ring 100 into filament placement chamber 54 throughfixed placing means located around entrance die 132. Fixed feeder ring100 is disposed around and fixedly attached to entrance die 132. Thehydraulically settable mixture passes from bore 130 of entrance die 132and into bore 134 of rotatable channel carriage 136. Filaments are fedthrough filament entry 58 and channel 60 and delivered to scoop end 62and then placed below the surface of the hydraulically settable matrix.

To achieve a helical or spiral configuration of filaments within thehydraulically settable matrix either rotatable feeder ring 102 or 104can be rotated while simultaneously delivering filaments from spools 108to the placing means which place the filaments in the matrix and rotatewith the rotatable feeder rings. Rotatable feeder ring 102 deliversfilaments to placing means located within rotatable channel carriage 136which is fixedly attached to rotatable feeder ring 102 by a lockingcollar 160.

Rotatable channel carriage 136 comprises a front section 162 having aflat side 164 and a convex side 166 with grooves 168 and furthercomprising a back section 170 having a flat side 172 and a concave side174. Convex side 166 of front section 162 and concave side 174 of backsection 170 are bolted together in a mating relationship.

The filament entry 70, channels 72 and nib ends 74 located withinrotatable channel carriage 136 comprise a placing means for placing thefilaments within the hydraulically settable matrix. Channels 78 areformed by grooves 168 in convex side 166 and by concave side 174 whenconvex side 166 and concave side 174 are mated. The angle at which thefilament enters into the hydraulically settable mixture can be varied byvarying the pitch of convex side 166 and concave side 168.

Locking collar 160 retains a ball bearing assembly 178 within the flatside of the front section 162 and another locking collar 180 retainsanother ball bearing assembly 182 within flat side 164 of the backsection 170. Each ball bearing assembly has a tubular neck 184 and a lip186. The ends of bore 134 extend within and are concentric with thetubular necks 184 of both ball bearing assemblies 178 and 182. Lip 186of ball bearing assembly 178 is positioned in a groove in clamp 124 witha lip 186 of entrance die 132. Ball bearing assembly 178 remainsrelatively stationary as rotatable channel carriage 136 rotates.

In the extrusion direction, the mixture is received from bore 130 ofrotatable channel carriage 136 and into bore 138 of another rotatablechannel carriage 140. Within bore 138, filaments are placed in thehydraulically settable mixture by the placing means comprising filamententry 70, channels 72 and nib ends 74 located within rotatable channelcarriage 140. The filaments are delivered to the placing means fromspools 108 on rotatable feeder ring 104 which is fixedly attached torotatable channel carriage 140 by a locking collar 188.

Rotatable channel carriage 140 is shown being structurally identical torotatable channel carriage 136. Rotatable channel carriage 140 comprisesa front section 190 having a flat side 192 and a convex side 194 withgrooves 96 and further comprising a back section 198 having a flat side200 and a concave side 202. Convex side 194 of front section 190 andconcave side 202 of back section 198 are bolted together in a matingrelationship.

The placing means located within rotatable channel carriage 140 havefilament entry 70, channels 72 and nib ends 74. Channels 72 are formedby grooves 204 in convex side 194 and by concave side 202 when convexside 194 and concave side 202 are mated. The angle at which the filamententers into the hydraulically settable mixture can be varied by varyingthe pitch of convex side 194 and concave side 202. The pitch of convexside 194 and concave side 202 can also be adjusted to reduce the strainon the filaments upon placement in the hydraulically settable mixtureand to counter the back pressure of filament placement chamber 54.

Ball bearing assembly 206 is retained within the flat side 192 of thefront section 190 by locking collar 188 and ball bearing assembly 208 isretained within flat side 200 of the back section 198 by locking collar210. Ball bearing assemblies 206 and 210 have tubular necks 184 and lips186. Rotating within necks 184 of ball bearing assemblies 206 and 208 isbore 138 of rotatable channel carriage 140 while ball bearing assemblies206 and 208 remain relatively stationary Lip 186 of ball bearingassembly 182 is positioned in a groove in clamp 124 with lip 186 of ballbearing assembly 206.

The structures of rotatable channel carriages 136 and rotatable feederring 102 are structurally identical to rotatable channel carriage 140and rotatable feeder ring 104, however, rotatable channel carriage 136and rotatable feeder ring 102 rotate in the opposite direction ofrotatable channel carriage 140 and rotatable feeder ring 104. Althoughthe structures are shown in an identical configuration, the structurescan also be different to vary the placement depth, the exit angle andthe winding angle.

The hydraulically settable mixture and the filament pass from bore 138of the rotatable channel carriage 140 into bore 142 of exit die 144which forms the end of filament placement chamber 54. Exit die 144 has alip 186 which is positioned in a groove of clamp 124 with lip 186 ofball bearing assembly 208. Ball bearing assembly 208 and exit die 144remain relatively stationary as rotatable channel carriage 140 rotates.

In operation of apparatus 50, as the hydraulically settable mixture isextruded through filament placement chamber 54 the filaments placed bythe placing means adhere to the hydraulically settable mixture at ornear the surface of the extruding mixture, thereby causing the filamentsto be drawn from the placing means as the mixture advances. Thefilaments can be delivered for placement within the matrix of an articleby one feeder ring to obtain a desired filament configuration or by morethan one feeder ring to obtain multiple configurations. A criss-crossconfiguration of filaments can be achieved when filaments are placedfrom placing means which are rotated with both rotatable feeder rings102 and 104. Additionally, a criss-cross configuration and a parallelconfiguration of filaments can be placed within a hydraulically settablematrix delivering filaments to placing means from fixed feeder ring 100and rotatable feeder rings 102 and 104.

Depicted in FIGS. 26, 27, 28 and 29 are perspective views of articles 66being continuously extruded as pipes by apparatus 50 to have variousconfigurations of filament within the pipes. The filament configurationsare revealed in FIGS. 26-29 by shadow lines. FIGS. 26-29 illustratesvarious embodiments of apparatus 50 as shown in FIGS. 22-25 and theability of the various embodiments to produce various configurations offilaments within an article.

FIG. 26 shows a pipe having filaments extending along the length of thepipe in a parallel configuration as placed by a set of fixed placingmeans circumferentially disposed around filament placement chamber 54 infixed channel carriage 214, which is shown in a cut-away view. A pipe isshown in FIG. 27 having filaments extending along the length of the pipein a helical or spiral configuration as placed by a set of rotatableplacing means circumferentially disposed around filament placementchamber 54 in rotatable channel carriage 136, which is shown in acut-away view.

FIG. 28 shows a pipe having filaments extending along the length of thepipe in a criss-cross configuration. Filaments are dispensed fromfilament spools 108 positioned on rotatable feeder ring 106 to rotatableplacing means located in rotatable channel carriage 140, shown in acut-away view. Rotatable feeder ring 102 is illustrated by shadow linesto indicate that filaments are being dispensed to another set ofrotatable placing means and placed in the mixture. FIG. 29 is similar toFIG. 28, however, apparatus 50 is shown with a fixed feeder ring 100illustrated by shadow lines to indicate that filaments are beingdispensed to a set of fixed placing means and placed in the mixture. Thepipe shown in FIG. 29 has a parallel and criss-cross configuration offilaments extending along the length of the pipe as placed by therespective sets of placing means. The embodiment shown in FIG. 29 canalso be utilized to achieve the same filament configurations as shown inFIGS. 26-28 by operating only one or two of the feeder rings inconjunction with the corresponding sets of placing means.

IV. EXAMPLES OF THE PREFERRED EMBODIMENTS.

To date, numerous tests have been performed comparing the rheologicaland extrusion properties of various hydraulically settable mixtures ofvarying composition. Below are specific examples of compositions whichhave been extruded according to the present invention. These actualexamples also include a description of hypothetically placing filamentswithin the hydraulically settable mixtures during extrusion.Additionally, a number of hypothetical, or "prophetic", examples havebeen included based on actual mix designs that have been extruded orwhich would be expected, based on experience, to possess the propertiesdescribed hereinafter. The actual examples are written in the pasttense, while the hypothetical examples are written in the present tensein order to distinguish between the two.

In general, the examples are directed to placing filaments inhydraulically settable mixtures which employ varying levels of waterdeficiency and particle packing efficiency, along with varying amountsof, for example, hydraulically settable binder, aggregates, fibers,rheology-modifying agents, and other admixtures in order to obtainmixtures having varying flow properties when extruded under pressure,and varying degrees of form-stability once the article has been extrudedand the pressure released.

EXAMPLES 1-9

Hydraulically settable mixtures having 4 kg of portland cement Type 1, 6kg fine silica sand, 50 g Tylose® FL 15002, and varying amounts of waterwere prepared and then extruded through a die using a piston extruder.The fine silica sand had a natural packing density of about 0.55 and aparticle size in the range from about 30-50 microns. When mixed withportland cement Type 1, which has an average particle size in a rangefrom about 10-25 microns, the resulting dry mixture had a particlepacking density of about 0.65, which represents only a moderate increaseover the natural packing density of each. The natural packed volume ofthe cement and sand was 5.504 liter, with a porosity of 1.924 liter.

The amount of water in the mixtures was varied as follows in order todetermine the extrudability of the mixture at varying levels of waterdeficiency:

    ______________________________________                                        Example  Water    % Deficient                                                                              Extrusion Pressure                               ______________________________________                                        1        3.0 kg   (55.9%)     15 psi                                          2        2.5 kg   (29.9%)     15 psi                                          3        1.924 kg 0%          45 psi                                          4        1.905 kg  1.0%      100 psi                                          5        1.65 kg  14.2%      300 psi                                          6        1.443 kg 25.0%      820 psi                                          7        0.962 kg 50.0%      1639 psi                                         8        0.60 kg  68.8%      2131 psi                                         9        0.40 kg  79.2%      3278 psi                                         ______________________________________                                    

In Examples 1 and 2, the numbers in parentheses under the heading "%Deficient" indicates that an excess of water was used. That is, morewater than the volume of interstitial space (or porosity, which was1.924 liter) was added. As a result, these mixtures were characterizedas "very fluid" and could not be extruded with sufficient form-stabilityso that the extruded objects would maintain their shape without externalsupport. Similarly, although Examples 3 and 4 were less fluid and werecharacterized as "very soft" they could not be extruded into form-stableobjects that would completely maintain their shape without externalsupport. However, as the amount of water was further decreased, therebyincreasing the water deficiency, the form-stability of the extrudedmaterial increased to the point where an extruded object would maintainits shape without external support.

The mixture of Example 5 was characterized as "soft" but could beextruded at relatively low pressure into an object having goodform-stability. The mixtures in Examples 6-9 could be extruded byincreasing the extrusion pressure as the amount of water was decreased,with increasing form-stability being observed as the amount of waterdecreased. As the water deficiency and extrusion was increased, thelevel of compaction of the mixture also increased, which resulted ingreater packing of the particles together and higher density of theextruded material. After each of the mixtures was allowed to harden, thehardened material for each example had the following tensile strengths,respectively, expressed in MPa: 2.4, 3.1, 5.2, 15.2, 28.2, 30.3, 32.2,35.0, and 38.0.

The placement of filaments within the mixtures substantially varies theproperties of the mixtures and the final hardened articles formedtherefrom, particularly the tensile strength of the articles. Anyfilaments can be used including fiberglass, aramid fibers, carbonfibers, graphite fibers, polyethylene fibers and other organic fibers.

The mixtures of Examples 5-9 were successfully extruded into honeycomb(i.e., multicellular) structures, bars, and window frames. The mixturesof Examples 6-9 were also extruded into pipes of varying wall thickness.The pipe extruded from the mixture of Example 7 had a wall thicknessthat was 25% of the pipe cavity; the pipe extruded from the mixture ofExample 8 had a wall thickness that was 15% of the pipe cavity; and thepipe extruded from the mixture of Example 9 had a wall thickness thatwas 10% of the pipe cavity. The wall thickness can be further reduced byreinforcing the pipe with filaments.

EXAMPLES 10-13

To the mixtures of Examples 5-9 are added the following amounts offiber, expressed as a percentage by volume of the total solids contentof the hydraulically settable mixture:

    ______________________________________                                               Example                                                                              Fiber                                                           ______________________________________                                               10     1%                                                                     11     2%                                                                     12     3%                                                                     13     4%                                                              ______________________________________                                    

The type of fiber that will be added depends on the properties andperformance criteria of the extruded article. In general, however,increasing the tensile strength of the fiber will increase the tensilestrength of the extruded article. Nevertheless, other factors such asaspect ratio, length, and reactivity with the hydraulically settablebinder will affect the level of anchoring or pull-out of the fiberswithin the hydraulically settable matrix when subjected to stresses andstrains. As the amount of fiber is increased, the tensile strength andductility of the hardened extruded article also increase. The tensilestrength and ductility of the article due to the fibers, however, isrelatively small when filaments are placed in the hydraulically settablematrix.

EXAMPLE 14

The procedures of Examples 1-9 were repeated except that the amount ofTylose® FL 15002 within the hydraulically settable mixture was increasedto 100 g prior to extrusion. The increased amount of Tylose® aided theextrusion process by increasing the lubrication between the particlesthemselves and between the particles and the extruder walls and diehead.In addition, the increased Tylose® increased the form-stability of theextruded articles somewhat, although not two-fold. The ability of themixture to pull a filament is not substantially effected by increasingthe amount of Tylose® as the viscosity is not greatly increased.

EXAMPLE 15

The procedures of Examples 1-9 were repeated except that 160 g ofsulfonated naphthalene-formaldehyde condensate was added to the mixtureas a dispersant. First the hydraulic cement, water, dispersant and atleast part of the aggregate were mixed together using a high shear mixerfor about 10 minutes. Afterward, the Tylose® FL 15,002 and the remainingaggregate, if any, were mixed into the mixture using a low shear mixer.The dispersant allowed for the obtaining of a more fluid mixture whilemaintaining the same level of water.

The resulting hydraulically settable mixtures have lower viscosity,which made them more easily extruded using lower pressures, compared tothe mixtures of Examples 1-9. However, the lower viscosity tends todecrease the ability of the mixture to pull filaments. Additionally, theextruded articles were generally less form stable than theircounterparts obtained in Examples 1-9. Nevertheless, significantly lesswater was required to obtain a mixture having the same level ofextrudability and form stability in the present example compared toExamples 1-9. This yielded final cured articles having higher strengthdue to the reduced amount of water within the hydraulically settablemixtures, according to the Strength Equation.

EXAMPLE 16

The procedures of Examples 1-9 and 15 were repeated, except that 0.8 kgof silica fume was also added to each of the mixtures. Because of thehigh specific surface area of silica fume, the mixtures which includedsilica fume had better dispersion, particularly where a dispersant wasadded to the mixture.

While the addition of silica fume would be expected to result in amixture requiring more water to obtain the same level of workability, itturns out that the extremely small particle size of the silica fumerelative to the other particles within the hydraulically settablemixtures greatly increased their particle packing densities.Consequently, the mixtures had significantly lower porosities, whichdecreased the amount of water needed to lubricate the particles. As aresult, the extrudability of the mixtures containing silica fume wassimilar to those which did not include silica fume. However, the silicafume increased the yield stress and cohesive nature of the mixtures,which increased the form stability of the extruded articles madetherefrom. The ability to pull filaments is also increased, however, itbecomes more difficult to control the placement of the filaments byincreasing the tension on the filaments. The pull-out effect on thefilaments in the hardened article is decreased as the filaments havegreater contact with the other components of the hydraulically settablestructural matrix.

In the following examples, the particle sizes of the silica sandaggregate were increased in order to increase the packing density of theresulting mixture. The increased particle packing densities that werethus obtained resulted in extruded articles of higher strength. Thisgoes against the conventional wisdom, which teaches the use of thefinest particle size available in order to increase the density, andhence the strength, the final hardened article. In contrast, byprogressively increasing the size of the silica sand particles, whichincreased the ratio of the size of the aggregate particle to the cementparticles to within the preferred and more preferred ranges, the densityof the mixture actually increased.

EXAMPLES 17-36

The same amounts and types of hydraulically settable binder andaggregate were used according to Examples 1-9, except that the amount ofadded water was varied in much smaller gradations as follows:

    ______________________________________                                        Example        Water   % Deficient                                            ______________________________________                                        17             3.0 kg  (55.73%)                                               18             2.8 kg  (45.35%)                                               19             2.6 kg  (34.97%)                                               20             2.4 kg  (24.59%)                                               21             2.2 kg  (14.20%)                                               22             2.0 kg   (3.82%)                                               23             1.8 kg   6.46%                                                 24             1.6 kg  16.94%                                                 25             1.4 kg  27.32%                                                 26             1.2 kg  37.71%                                                 27             1.0 kg  48.09%                                                 28             0.9 kg  53.23%                                                 29             0.8 kg  58.47%                                                 30             0.7 kg  63.66%                                                 31             0.6 kg  68.85%                                                 32             0.5 kg  74.04%                                                 33             0.4 kg  79.24%                                                 34             0.3 kg  84.43%                                                 35             0.2 kg  89.62%                                                 36             0.1 kg  94.81%                                                 ______________________________________                                    

The extrusion pressures needed to extrude the mixtures of these exampleswere similar to those needed to extrude the mixtures of Examples 1-9. Asabove, the mixtures in Examples 17-22 were too fluid to have adequateform-stability after being extruded. In addition, because they had anexcess of water initially, they exhibited relatively low strengthaccording to the Strength Equation. While the mixture of Example 23could be extruded, only articles of larger cross section and simpleshape were able to maintain their shape without external support. Themixtures of Examples 24-33 could be extruded within about the same rangeof pressures as the mixtures of Examples 5-9. However, the mixtures ofExamples 34-36 were unable to be extruded using the extruding equipmentavailable to the inventors. Mixtures which are too fluid do not provideadequate viscosity to pull filaments after filaments are placed in suchfluid mixtures.

EXAMPLES 37-53

Hydraulically settable mixtures having 4 kg of portland cement Type 1, 6kg silica sand, 50 g Tylose®, and varying amounts of water were preparedand then extruded through a die using a piston extruder. The silica sandhad a natural packing density of about 0.55 and a particle size withinthe range from about 50-80 microns. When mixed with portland cement Type1, which has a particle size within the range from about 10-25 microns,the resulting dry mixture had a particle packing density of about 0.7,which represents a better increase over the natural packing density ofeach compared to what was obtained in Examples 1-9.

The mount of water in the mixtures was varied as follows in order todetermine the extrudability of the mixture at varying levels of waterdeficiency:

    ______________________________________                                        Example        Water   % Deficient                                            ______________________________________                                        37             2.4 kg  (56.53%)                                               38             2.2 kg  (43.49%)                                               39             2.0 kg  (30.44%)                                               40             1.8 kg  (17.40%)                                               41             1.6 kg   (4.35%)                                               42             1.4 kg   8.69%                                                 43             1.2 kg  21.73%                                                 44             1.0 kg  34.78%                                                 45             0.9 kg  41.30%                                                 46             0.8 kg  47.82%                                                 47             0.7 kg  54.34%                                                 48             0.6 kg  60.87%                                                 49             0.5 kg  67.39%                                                 50             0.4 kg  73.91%                                                 51             0.3 kg  80.43%                                                 52             0.2 kg  86.96%                                                 53             0.1 kg  93.48%                                                 ______________________________________                                    

In Examples 37-41, the number in parentheses under the heading "%Deficient" indicates the amount of excess water that was used. As above,these mixtures were "very fluid" and could not be extruded withsufficient form-stability so that an extruded object would maintain itsshape without external support. The mixtures of Examples 42-50 were ableto be extruded into a variety of form-stable articles as above,including honeycomb structures, bars, and window frames. Because of thehigher particle packing efficiencies of the mixtures of Examples 37-53compared to those of Examples 1-9, holding the water constant resultedin mixtures having decreased water deficiency and, hence, greaterflowability and lower viscosity. The higher particle packing alsoincreases the anchoring of filaments in a hardened article formed fromsuch mixtures as the filaments have greater contact with the othercomponents of the hydraulically settable structural matrix.

As the amount of water deficiency increased, pipes of increasinglythinner walls could be extruded. In addition, the final hardenedextruded articles had higher strength compared to the articles extrudedfrom the mixtures having a lower particle packing density, whichcomports with the Strength Equation. Pipes having even thinner walls canbe designed by placing filaments within the mixtures.

However, as the amount of water fell below 0.4 kg and the waterdeficiency increased to above about 75%, the mixtures could not beextruded using the equipment available, although it is believed thatusing a higher pressure extruder would make it possible, though lesspractical, to extrude such mixtures. Therefore, the mixtures in Examples51-53 could not be extruded.

From these examples it can be seen that increasing the packing densityof the solid particles while keeping the amount of added water constantresults in a mixture having less water deficiency. This allows for theextrusion of a higher packed mixture at a lower pressure for the sameamount of water. Additionally, increasing the packing density increasesthe frictional contact with filaments, which results in an increasedability to pull filaments placed within a mixture.

EXAMPLES 54-67

The hydraulically settable mixtures of Examples 40-53 are repeatedexcept that silica sand having particle sizes in the range of about60-120 microns is used. The resulting particle packing density of theresulting sand and cement mixture is about 0.75. Keeping the amount ofadded water constant according to Examples 40-53 yields mixtures havingthe following amounts of water deficiency:

    ______________________________________                                        Example        Water   % Deficient                                            ______________________________________                                        54             1.8 kg  (50.94%)                                               55             1.6 kg  (34.17%)                                               56             1.4 kg  (17.40%)                                               57             1.2 kg   (0.63%)                                               58             1.0 kg  16.14%                                                 59             0.9 kg  24.53%                                                 60             0.8 kg  32.91%                                                 61             0.7 kg  41.30%                                                 62             0.6 kg  49.69%                                                 63             0.5 kg  58.07%                                                 64             0.4 kg  66.46%                                                 65             0.3 kg  74.84%                                                 66             0.2 kg  83.23%                                                 67             0.1 kg  91.61%                                                 ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures, which may reduce thestrain on filaments as the filaments are placed within a mixture andincreases the ability to control placement based on filament tension. Inaddition, the final hardened extruded article has higher strengthaccording to the Strength Equation. However, the mixtures of Examples54-57 lack form-stability after being extruded, while the mixtures ofExamples 58-65 can be extruded into a number of articles, includingthose listed above. Finally, the mixtures of Examples 66 and 67 are toodry and viscous to be extruded using the equipment available. The higherparticle packing density also increases the anchoring of filaments in ahardened article formed from such mixtures as the filaments have greatercontact with the other components of the hydraulically settablestructural matrix.

EXAMPLES 68-79

The hydraulically settable mixtures obtained in Examples 25-36 arealtered by decreasing the amount of fine silica sand to 4 kg and adding2 kg of precipitated calcium carbonate having an average particle sizeof about 1 micron. This results in a hydraulically settable mixturehaving a particle packing density of about 0.8. The resulting waterdeficiencies for a given amount of water are as follows:

    ______________________________________                                        Example        Water   % Deficient                                            ______________________________________                                        68             1.4 kg  (56.53%)                                               69             1.2 kg  (34.17%)                                               70             1.0 kg  (11.81%)                                               71             0.9 kg   (0.63%)                                               72             0.8 kg  10.55%                                                 73             0.7 kg  21.73%                                                 74             0.6 kg  32.91%                                                 75             0.5 kg  44.10%                                                 76             0.4 kg  55.28%                                                 77             0.3 kg  66.46%                                                 78             0.2 kg  77.64%                                                 79             0.1 kg  88.82%                                                 ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures, which may reduce thestrain on filaments as the filaments are placed within a mixture andincrease the ability to control placement based on filament tension. Inaddition, the final hardened extruded article has higher strength,according to the Strength Equation. The higher particle packing densityalso increases the anchoring of filaments in a hardened article formedfrom such mixtures as the filaments have greater contact with the othercomponents of the hydraulically settable structural matrix.

EXAMPLES 80-89

The hydraulically settable mixtures obtained in Examples 44-53 arealtered by decreasing the amount of silica sand to 4 kg and adding 2 kgof precipitated calcium carbonate having an average particle size ofabout 1 micron. This results in a hydraulically settable mixture havinga particle packing density of about 0.85. The resulting waterdeficiencies for a given amount of water are as follows:

    ______________________________________                                        Example        Water   % Deficient                                            ______________________________________                                        80             1.0 kg  (58.40%)                                               81             0.9 kg  (42.56%)                                               82             0.8 kg  (26.72%)                                               83             0.7 kg  (10.88%)                                               84             0.6 kg   4.96%                                                 85             0.5 kg  20.80%                                                 86             0.4 kg  36.64%                                                 87             0.3 kg  52.48%                                                 88             0.2 kg  68.32%                                                 89             0.1 kg  84.16%                                                 ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures which may reduce the strainon filaments as the filaments are placed within a mixture and increasethe ability to control placement based on filament tension. In addition,the final hardened extruded article has higher strength, according tothe Strength Equation. The higher particle packing density alsoincreases the anchoring of filaments in a hardened article formed fromsuch mixtures as the filaments have greater contact with the othercomponents of the hydraulically settable structural matrix.

EXAMPLES 90-95

The hydraulically settable mixtures obtained in Examples 62-67 arealtered by decreasing the amount of silica sand to 4 kg and adding 2 kgof precipitated calcium carbonate having an average particle size ofabout 1 micron. This results in a hydraulically settable mixture havinga particle packing density of about 0.9. The resulting waterdeficiencies for a given amount of water are as follows:

    ______________________________________                                        Example        Water   % Deficient                                            ______________________________________                                        90             0.6 kg  (46.06%)                                               91             0.5 kg  (21.71%)                                               92             0.4 kg   2.63%                                                 93             0.3 kg  26.97%                                                 94             0.2 kg  51.31%                                                 95             0.1 kg  75.66%                                                 ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures which may reduce the strainon filaments as the filaments are placed within a mixture and increasethe ability to control placement based on filament tension. In addition,the final hardened extruded article has higher strength according to theStrength Equation. The higher particle packing density also increasesthe anchoring of filaments in a hardened article formed from suchmixtures as the filaments have greater contact with the other componentsof the hydraulically settable structural matrix.

EXAMPLE 96

The procedures of Examples 1-9 are repeated, except that the averageparticle size is decreased while maintaining the same level of particlepacking density and water deficiency. The resulting hydraulicallysettable mixtures exhibit greater pseudo-plastic behavior. In otherwords, the apparent viscosities of the mixtures having a lower averageparticle size decreases for a given shear rate, while the yield stressincreases. This results in mixtures which may be extruded under lowerpressure while exhibiting greater form stability. Extrusion under lowerpressure may reduce the strain on filaments as the filaments are placedwithin a mixture and increase the ability to control placement based onfilament tension. The form stability of such mixtures is substantiallyincreased by filaments placed within the mixtures.

EXAMPLE 97

The procedures of Examples 90-95 are repeated, except that the extrudedarticles are cured by autoclaving at 400° C. and 24 bars of pressure for12 hours. The final cured articles have compressive strength of about800 MPa and a tensile strength of about 100 MPa. The tensile strength ofthe final cured articles is substantially increased by filaments placedwithin the mixture.

EXAMPLE 98

The procedures of Examples 1-9 are repeated, except that 25 g of Tylose®4000 are added as lubricant. The resulting hydraulically settablemixtures have greater flowability and result in extruded articles havinga better surface finish without substantially affecting the ability ofthe mixture to pull filaments. The strength properties remainapproximately the same.

EXAMPLE 99

The procedures of Examples 1-9 are repeated, except that 25 g of calciumor magnesium stearate are added as lubricant. The resultinghydraulically settable mixtures have greater flowability and result inextruded articles having a better surface finish without substantiallyaffecting the ability of the mixture to pull filaments. The strengthproperties remain approximately the same.

EXAMPLE 100

The procedures of Examples 1-9 are repeated, except that 25 g ofpolyethylene glycol having an average molecular weight of about 35,000are added as lubricant. The resulting hydraulically settable mixtureshave greater flowability and result in extruded articles having a bettersurface finish without substantially affecting the ability of themixture to pull filaments. The strength properties remain approximatelythe same.

EXAMPLE 101

An extrudable hydraulically settable mixture is formed using thefollowing components:

    ______________________________________                                        Fly ash                 90 g                                                  Portland Cement         10 g                                                  NaOH                    10 g                                                  Water                   20 g                                                  ______________________________________                                    

The sodium hydroxide raises the pH of the aqueous phase of thehydraulically settable mixture to about 14, which activates the fly ashso that it behaves as a hydraulically settable binder. Portland cementis added in order to increase the compressive strength of the finalcured product to about 20 MPa and the tensile strength to about 105 MPa.Because of the low cost of fly ash, the mixture of this example is lessexpensive than those containing higher levels of portland cement andconventional aggregates. Of course, where lower strengths areacceptable, the portland cement may be further reduced or eliminatedaltogether. The fly ash also increases the frictional contact with thefilaments, which increases the ability of the mixture to pull thefilaments and better anchors the filaments within the hydraulicallysettable matrix.

EXAMPLE 102

An extrudable hydraulically settable mixture is formed using thefollowing components:

    ______________________________________                                        Portland White Cement                                                                            4.0        kg                                              Fine Sand          6.0        kg                                              Water              1.5        kg                                              Tylose ® FL 15002                                                                            200        g                                               ______________________________________                                    

The hydraulically settable mixture is formed by mixing the ingredientstogether for 10 minutes using a high speed mixer to obtain a veryhomogeneous mixture. Thereafter, the mixture is extruded into a varietyof multi-cell structures, including "honeycomb" structures, which havevery high compressive strength, particularly in light of the open cellnature of the extruded object.

Because of the multi-cell structure, the cured material is much morelightweight than comparable solid extruded objects made from the samehydraulically settable mixtures. The block density of the multi-cellstructures is only 1.02 g/cm³. Moreover, the cured materials have acompressive strength of about 75 MPa and a tensile strength of about 28MPa. Depending upon the amount of space within the multi-cell structure,the block density can easily range anywhere from between about 0.5 g/cm³to about 1.6 g/cm³. The tensile strength can be substantially increasedby filaments placed within the mixture which permits even lower blockdensities.

EXAMPLES 103-105

Extrudable hydraulically settable mixtures are formed according toExample 102, except that abaca fiber is added to the mixtures in varyingamounts as follows (measured by volume):

    ______________________________________                                        Example      Abaca Fiber                                                      ______________________________________                                        103          1%                                                               104          2%                                                               105          3%                                                               ______________________________________                                    

The resulting extruded multi-cell structures have greater strengths,both in the green state and after they are cured, than the structures ofExample 102. Moreover, the multi-cell structures formed in theseexamples are more ductile and less brittle, particularly as more fiberis added to the hydraulically settable mixture. Placement of filamentswithin the mixtures further increases the ductility and reduces thebrittleness of the structures.

EXAMPLES 106-108

Extrudable hydraulically settable mixtures are formed according toExample 102, except that glass fiber is added to the mixtures in varyingamounts as follows (measured by volume):

    ______________________________________                                               Example                                                                              Glass Fiber                                                     ______________________________________                                               106    1%                                                                     107    2%                                                                     108    3%                                                              ______________________________________                                    

The resulting extruded multi-cell structures have greater strengths,both in the green state and after they are cured, than the structures ofExample 102. Moreover, the multi-cell structures formed in theseexamples are more ductile and less brittle, particularly as more fiberis added to the hydraulically settable mixture. Similarly, placement offilaments within the mixtures substantially increases the ductility anddecreases the brittleness.

The following examples demonstrate how the strength of an extrudedhydraulically settable mixture increases or decreases as the followingvariables are varied: particle packing density, water to cement ratio,and amount of cement as a percentage of the solids content of themixture.

EXAMPLES 109-114

Extrudable hydraulically settable mixtures are formed which have 1.0 kgportland cement and 6.0 kg sand. In each mixture the portland cementcomprises 14.3% by weight of the dry mixture. The particle sizes of thesand are varied in order to yield mixtures having particle packingdensities which vary from 0.65 to 0.90 in increments of 0.05. Inaddition, the amount of water that is added is varied in order to yielda mixture having the desired level of water deficiency. In this firstset of examples, the water deficiency is 50%.

As will be shown, the compressive strength of a hydraulically settablemixture having a constant weight percentage of portland cement and sandincreases if either (1) the particle packing density is increased whilemaintaining a constant level of water deficiency or (2) the level ofwater deficiency is increased while maintaining a constant packingdensity. The amount of water is expressed in kg, while the compressivestrength is expressed in MPa. The phrase "W/C Ratio" is shorthand forwater to cement ratio.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        109    0.65         0.71     0.71     24                                      110    0.70         0.56     0.56     33                                      111    0.75         0.44     0.44     47                                      112    0.80         0.33     0.33     69                                      113    0.85         0.23     0.23     103                                     114    0.90         0.15     0.15     160                                     ______________________________________                                    

These examples clearly demonstrate that the strength of an extrudedarticle will greatly increase as the particle packing density isincreased, even while the absolute level of cement and sand are heldconstant. This correlates to the Strength Equation because as theparticle packing density is increased both the amount of air and waterwithin the mixture are decreased. However, because the amount of waterdeficiency is held constant, the mixtures have similar levels ofworkability and may be extruded using similar extrusion pressures. Theincreased particle packing increases the frictional contact between thefilaments and other components of the hydraulically settable structuralmatrix, which increases the ability of the mixtures to pull thefilaments and better anchors the filaments within the hydraulicallysettable structural matrix.

EXAMPLES 115-120

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        115    0.65         0.57     0.57     31                                      116    0.70         0.45     0.45     43                                      117    0.75         0.35     0.35     59                                      118    0.80         0.26     0.26     84                                      119    0.85         0.19     0.19     121                                     120    0.90         0.12     0.12     182                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 121-126

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        121    0.65         0.42     0.42     42                                      122    0.70         0.34     0.34     57                                      123    0.75         0.26     0.26     76                                      124    0.80         0.20     0.20     105                                     125    0.85         0.14     0.14     146                                     126    0.90         0.09     0.09     209                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 127-132

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        127    0.65         0.28     0.28     60                                      128    0.70         0.23     0.23     78                                      129    0.75         0.18     0.18     102                                     130    0.80         0.13     0.13     134                                     131    0.85         0.09     0.09     179                                     132    0.90         0.06     0.06     243                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 133-138

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        133    0.65         0.14     0.14     94                                      134    0.70         0.11     0.11     116                                     135    0.75         0.09     0.09     143                                     136    0.80         0.07     0.07     179                                     137    0.85         0.05     0.05     224                                     138    0.90         0.03     0.03     285                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Comparison of the resultsobtained in Examples 109-138 demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. This clearly demonstrates that in order tosimultaneously achieve high strength and high workability in a givenmixture, it is advantageous to increase the particle packing densityrather than increase the level of water in order to increase theflowability of the mixture under pressure.

The next set of examples is substantially similar to Examples 109-138,except that the amount of portland cement is increased to 25% by weightof the dry mixtures. The purpose of these examples is to demonstratethat only modest increases of strength are attained by increasing theamount of hydraulically settable binder, while the most dramaticincreases in strength are achieved by increasing the particle packingdensity and decreasing the amount of water within the mixtures.

EXAMPLES 139-144

Extrudable hydraulically settable mixtures are formed which have 2.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        139    0.65         0.79     0.40     52                                      140    0.70         0.63     0.32     69                                      141    0.75         0.49     0.25     90                                      142    0.80         0.37     0.18     120                                     143    0.85         0.26     0.13     160                                     144    0.90         0.16     0.08     215                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 145-150

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        145    0.65         0.63     0.32     65                                      146    0.70         0.50     0.25     83                                      147    0.75         0.39     0.20     107                                     148    0.80         0.29     0.15     138                                     149    0.85         0.21     0.10     179                                     150    0.90         0.13     0.07     234                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 151-156

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        151    0.65         0.48     0.24     82                                      152    0.70         0.38     0.19     103                                     153    0.75         0.29     0.15     129                                     154    0.80         0.22     0.11     162                                     155    0.85         0.16     0.08     203                                     156    0.90         0.10     0.05     255                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 157-162

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        157    0.65         0.32     0.16     109                                     158    0.70         0.25     0.13     132                                     159    0.75         0.20     0.10     159                                     160    0.80         0.15     0.07     192                                     161    0.85         0.10     0.05     231                                     162    0.90         0.07     0.03     279                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 163-168

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        163    0.65         0.16     0.08     150                                     164    0.70         0.13     0.06     173                                     165    0.75         0.10     0.05     200                                     166    0.80         0.07     0.04     231                                     167    0.85         0.05     0.03     267                                     168    0.90         0.03     0.02     308                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Examples 139-168 demonstrate the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. Although increasing the amount of portland cementwithin the mixtures of Examples 139-168 causes an increase in theoverall strength of the mixtures, the increase is less dramatic thanincreasing the particle packing density and decreasing the level ofwater within the mixtures.

The next set of examples is substantially similar to Examples 139-168,except that the amount of portland cement is increased to 33% by weightof the dry mixtures.

EXAMPLES 169-174

Extrudable hydraulically settable mixtures are formed which have 3.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        169    0.65         0.88     0.29     74                                      170    0.70         0.70     0.23      94                                     171    0.75         0.54     0.18     118                                     172    0.80         0.41     0.14     150                                     173    0.85         0.29     0.10     189                                     174    0.90         0.18     0.06     240                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 175-180

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        175    0.65         0.70     0.23     89                                      176    0.70         0.56     0.19     111                                     177    0.75         0.43     0.14     137                                     178    0.80         0.33     0.11     169                                     179    0.85         0.23     0.08     208                                     180    0.90         0.14     0.05     256                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 181-186

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        181    0.65         0.53     0.18     109                                     182    0.70         0.42     0.14     133                                     183    0.75         0.33     0.11     160                                     184    0.80         0.24     0.08     192                                     185    0.85         0.17     0.06     229                                     186    0.90         0.11     0.04     274                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the as the amount of water is reduced. Increasing thecompressive strength by reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 187-192

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        187    0.65         0.35     0.12     138                                     188    0.70         0.28     0.09     162                                     189    0.75         0.22     0.07     189                                     190    0.80         0.16     0.05     220                                     191    0.85         0.12     0.04     254                                     192    0.90         0.07     0.02     294                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the amount of water is reduced. Increasing the compressivestrength by reducing the amount of water may be useful to offset anytendency of the filaments to decrease the compressive strength of thefinal hardened articles.

EXAMPLES 193-198

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        193    0.65         0.18     0.06     180                                     194    0.70         0.14     0.05     203                                     195    0.75         0.11     0.04     227                                     196    0.80         0.08     0.03     254                                     197    0.85         0.06     0.02     283                                     198    0.90         0.04     0.01     316                                     ______________________________________                                    

Comparison of the strengths of the different compositions of Examples169-198 as a function of particle packing demonstrates the closerelationship between strength and the absolute level of water within thehydraulically settable mixture. Although increasing the amount ofportland cement within the mixtures of Examples 169-198 causes anincrease in the overall strength of the mixtures, the increase is lessdramatic than increasing the particle packing density and decreasing thelevel of water within the mixtures.

The next set of examples is substantially similar to Examples 169-198,except that the amount of portland cement is increased to 40% by weightof the dry mixtures.

EXAMPLES 199-204

Extrudable hydraulically settable mixtures are formed which have 4.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        199    0.65         0.96     0.24     90                                      200    0.70         0.77     0.19     111                                     201    0.75         0.60     0.15     138                                     202    0.80         0.45     0.11     169                                     203    0.85         0.32     0.08     208                                     204    0.90         0.20     0.05     254                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 205-210

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        205    0.65         0.77     0.19     106                                     206    0.70         0.61     0.15     129                                     207    0.75         0.48     0.12     156                                     208    0.80         0.36     0.09     188                                     209    0.85         0.25     0.06     225                                     210    0.90         0.16     0.04     269                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 211-216

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        211    0.65         0.58     0.14     128                                     212    0.70         0.46     0.11     152                                     213    0.75         0.36     0.09     179                                     214    0.80         0.27     0.07     210                                     215    0.85         0.19     0.05     245                                     216    0.91         0.12     0.03     284                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 217-222

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        217    0.65         0.39     0.10     158                                     218    0.70         0.31     0.08     181                                     219    0.75         0.24     0.06     207                                     220    0.80         0.18     0.04     236                                     221    0.85         0.13     0.03     267                                     222    0.90         0.08     0.02     301                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 223-228

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        223    0.65         0.19     0.05     199                                     224    0.70         0.15     0.04     220                                     225    0.75         0.12     0.03     243                                     226    0.80         0.09     0.02     267                                     227    0.85         0.06     0.02     292                                     228    0.90         0.04     0.01     320                                     ______________________________________                                    

Comparison of the strengths of the different compositions of Examples199-228 as a function of particle packing demonstrates the closerelationship between strength and the absolute level of water within thehydraulically settable mixture. Although increasing the amount ofportland cement within the mixtures of Examples 199-228 causes anincrease in the overall strength of the mixtures, the increase is lessdramatic than increasing the particle packing density and decreasing thelevel of water within the mixtures.

The next set of examples is substantially similar to Examples 199-228,except that the amount of portland cement is increased to 45.5% byweight of the dry mixtures.

EXAMPLES 229-234

Extrudable hydraulically settable mixtures are formed which have 5.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        229    0.65         0.05     0.21     102                                     230    0.70         0.83     0.17     125                                     231    0.75         0.65     0.13     152                                     232    0.80         0.49     0.10     183                                     233    0.85         0.34     0.07     220                                     234    0.90         0.22     0.04     263                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 235-240

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        235    0.65         0.84     0.17     120                                     236    0.70         0.67     0.13     143                                     237    0.75         0.52     0.10     170                                     238    0.80         0.39     0.08     201                                     239    0.85         0.27     0.05     236                                     240    0.90         0.17     0.03     276                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 241-246

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        241    0.65         0.63     0.13     142                                     242    0.70         0.50     0.10     166                                     243    0.75         0.39     0.08     193                                     244    0.80         0.29     0.06     222                                     245    0.85         0.21     0.04     254                                     246    0.90         0.13     0.03     291                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 247-252

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        247    0.65         0.42     0.08     172                                     248    0.70         0.33     0.07     195                                     249    0.75         0.26     0.05     220                                     250    0.80         0.19     0.04     246                                     251    0.85         0.14     0.03     275                                     252    0.90         0.09     0.02     306                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 253-258

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        253    0.65         0.21     0.04     211                                     254    0.70         0.17     0.03     232                                     255    0.75         0.13     0.03     253                                     256    0.80         0.10     0.02     275                                     257    0.85         0.07     0.01     298                                     258    0.90         0.04     0.01     322                                     ______________________________________                                    

Comparison of the strengths of the different compositions of Examples229-258 as a function of particle packing demonstrates the closerelationship between strength and the absolute level of water within thehydraulically settable mixture. Although increasing the amount ofportland cement within the mixtures of Examples 229-258 causes anincrease in the overall strength of the mixtures, the increase is lessdramatic than increasing the particle packing density and decreasing thelevel of water within the mixtures.

The next set of examples is substantially similar to Examples 229-258,except that the amount of portland cement is increased to 50% by weightof the dry mixtures.

EXAMPLES 259-264

Extrudable hydraulically settable mixtures are formed which have 6.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                              Strength                                ______________________________________                                        259    0.65         1.13     0.19     112                                     260    0.70         0.90     0.15     135                                     261    0.75         0.70     0.12     162                                     262    0.80         0.53     0.09     193                                     263    0.85         0.37     0.06     229                                     264    0.90         0.23     0.04     270                                     ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 265-270

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        265    0.65         0.91     0.15    130                                      266    0.70         0.72     0.12    154                                      267    0.75         0.56     0.09    181                                      268    0.80         0.42     0.07    211                                      269    0.85         0.30     0.05    244                                      270    0.90         0.19     0.03    282                                      ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 271-276

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        271    0.65         0.68     0.11    153                                      272    0.70         0.54     0.09    176                                      273    0.75         0.42     0.07    202                                      274    0.80         0.32     0.05    231                                      275    0.85         0.22     0.04    261                                      276    0.90         0.14     0.02    295                                      ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 277-282

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        277    0.65         0.45     0.08    182                                      278    0.70         0.36     0.06    204                                      279    0.75         0.28     0.05    228                                      280    0.80         0.21     0.04    254                                      281    0.85         0.15     0.02    280                                      282    0.90         0.09     0.02    309                                      ______________________________________                                    

The compressive strength of the hydraulically settable mixturesincreases as the particle packing increases and as the amount of wateris reduced. Increasing the compressive strength by increasing theparticle packing and reducing the amount of water may be useful tooffset any tendency of the filaments to decrease the compressivestrength of the final hardened articles.

EXAMPLES 283-288

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        283    0.65         0.23     0.04    221                                      284    0.70         0.18     0.03    240                                      285    0.75         0.14     0.02    260                                      286    0.80         0.11     0.02    280                                      287    0.85         0.07     0.01    302                                      288    0.90         0.05     0.01    324                                      ______________________________________                                    

Comparison of the strengths of the different compositions of Examples259-288 as a function of particle packing demonstrates the closerelationship between strength and the absolute level of water within thehydraulically settable mixture. Although increasing the amount ofportland cement within the mixtures of Examples 259-288 causes anincrease in the overall strength of the mixtures, the increase is lessdramatic than increasing the particle packing density and decreasing thelevel of water within the mixtures.

The next group of examples illustrates how the overall particle packingdensity of a two-component system (i.e., portland cement and sand) isaffected by the natural packing densities of the sand component and theportland cement component. Using the information contained in theseexamples would allow one of ordinary skill in the art to designhydraulically settable mixtures having the particle packing densities ofthe compositions set forth above in Examples 109-288. As shown below,the resulting particle packing density is affected not only by theindividual natural packing densities for the cement and sand componentsbut also by the average particle diameter of the cement and sandcomponents, respectively.

Note that different sand aggregates may have the same average diameterand yet have greatly varying packing densities. The natural packingdensity of an aggregate of a given average diameter will increase ordecrease depending on the distribution of particle diameters away fromthe mean diameter. In general, the greater the size variation among theparticles the greater the natural packing density of a given aggregate.

EXAMPLES 289-294

Hydraulically settable mixtures are formed which contain 1.0 kg portlandcement and 6.0 kg sand, yielding mixtures having 14.3% cement and 85.7%sand aggregate by weight of the dry components. The portland cement hasan average particle size of 15 microns and a natural packing density of0.580. Five different types of sand aggregate categorized on the basisof average diameter are selected to yield the desired overall packingdensity of the dry mixture. The five different aggregates, which shallbe referred to as "Aggregate 1", "Aggregate 2" and so on, have averageparticle diameters of 0.1 mm, 0.2 mm, 0.5 mm, 1.0 mm, and 1.25mm,respectively.

Each of the five types of sand aggregate is further distinguished on thebasis of natural packing density, as set forth below. The followingtable illustrates the effect on the overall particle packing density ofmixing the five different types of aggregates having varying particlepacking densities with the portland cement described above. The term"Aggregate" is abbreviated as "Agg"; the overall packing density isabbreviated as "Density"; and the numbers below each of the Aggregateheadings is the natural packing density for a given aggregate.

    ______________________________________                                        Example Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                              ______________________________________                                        289     0.65     0.595   0.586 0.579 0.577 0.577                              290     0.70     0.644   0.633 0.623 0.622 0.622                              291     0.75     0.696   0.682 0.673 0.670 0.669                              292     0.80     0.755   0.738 0.726 0.722 0.722                              293     0.85     0.828   0.806 0.791 0.786 0.785                              294     0.90     N/A     0.945 0.918 0.907 0.905                              ______________________________________                                    

As illustrated by these examples, greater overall particle packingdensity can be achieved either by keeping the average diameter of theaggregate constant while increasing the natural packing density of theaggregate, or by keeping the natural packing density constant andincreasing the average diameter of the aggregate. The increased packingeffect using the latter method is caused by the increase in variancebetween the average aggregate particle size and cement particle size.However, varying the natural packing density of a given aggregateappears to yield the greater increase in overall packing density. Theincreased particle packing increases the frictional contact between thefilaments and other components of the hydraulically settable structuralmatrix which increases the ability of the mixtures to pull the filamentsand better anchors the filaments within the hydraulically settablestructural matrix.

EXAMPLES 295-298

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 2.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 25% cement and 75% sand aggregate byweight of the dry components. The average particle size of the portlandcement and the five different sand aggregate types of the followingexamples are the same as in Examples 289-294.

    ______________________________________                                        Example Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                              ______________________________________                                        295     0.65     0.554   0.536 0.524 0.521 0.520                              296     0.70     0.612   0.589 0.575 0.570 0.569                              297     0.75     0.683   0.654 0.635 0.628 0.627                              298     0.80     0.785   0.745 0.718 0.708 0.707                              ______________________________________                                    

As illustrated in these examples, as the quantity of portland cement isincreased, the difficulty of creating mixtures from a two-componentsystem which have high overall packing density also increases. This isbecause of the general uniformity of particle sizes of the portlandcement compared to the sand aggregate. Greater particle uniformitygenerally decreases the ability to achieve higher particle packingdensities.

EXAMPLES 299-302

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 3.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 33.3% cement and 66.7% sandaggregate by weight of the dry components. The average particle size ofthe portland cement and the five different sand aggregate types of thefollowing examples are the same as in Examples 289-294.

    ______________________________________                                        Example Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                              ______________________________________                                        299     0.65     0.529   0.504 0.488 0.483 0.482                              300     0.70     0.601   0.568 0.547 0.540 0.538                              301     0.75     0.709   0.661 0.629 0.618 0.616                              302     0.80     0.950   0.915 0.849 0.816 0.809                              ______________________________________                                    

EXAMPLES 303-305

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 4.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 40% cement and sand aggregate byweight of the dry components. The average particle size of the portlandcement and the five different sand aggregate types of the followingexamples are the same as in Examples 289-294.

    ______________________________________                                        Example Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                              ______________________________________                                        303     0.65     0.515   0.483 0.462 0.456 0.454                              304     0.70     0.609   0.562 0.533 0.523 0.522                              305     0.75     0.792   0.719 0.662 0.643 0.639                              ______________________________________                                    

EXAMPLES 306-308

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 5.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 45.5% cement and 54.5% sandaggregate by weight of the dry components. The average particle size ofthe portland cement and the five different sand aggregate types of thefollowing examples are the same as in Examples 289-294.

    ______________________________________                                        Example Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                              ______________________________________                                        306     0.65     0.508   0.468 0.444 0.435 0.434                              307     0.70     0.634   0.571 0.531 0.518 0.515                              308     0.75     N/A     N/A   0.894 0.835 0.819                              ______________________________________                                    

EXAMPLES 309-310

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 6.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 50% cement and 50% sand aggregate byweight of the dry components. The average particle size of the portlandcement and the five different sand aggregate types of the followingexamples are the same as in Examples 289-294.

    ______________________________________                                        Example Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                              ______________________________________                                        309     0.65     0.507   0.459 0.430 0.421 0.419                              310     0.70     0.682   0.599 0.543 0.525 0.521                              ______________________________________                                    

EXAMPLES 311-316

Hydraulically settable articles containing spiral wound filaments wereproduced using conventional methods of filament winding (i.e., a greenhydraulically settable mixture was shaped in the form of a tube around amandrel, after which filaments were wound around and through theinterior of the mixture). The percentage of filaments wound around andinto the hydraulically settable articles was incrementally increased,while the winding angle was held constant at 45° in order to measure theeffect of filament concentration on the burst strength of the filamentwound articles. As quantified below, the initial input of 3.0% filamentscaused a dramatic increase in burst strength. Thereafter, the burststrength continued to increase, but less dramatically, as the percentageof filaments was further increased.

    ______________________________________                                        Example       Filament    Burst Strength                                      ______________________________________                                        311           0%           7 N/mm.sup.2                                       312           3.0%        34 N/mm.sup.2                                       313           4.5%        37 N/mm.sup.2                                       314           6.0%        38 N/mm.sup.2                                       315           7.5%        44 N/mm.sup.2                                       316           9.0%        46 N/mm.sup.2                                       ______________________________________                                    

The burst strength of each article as a function of the percentage offilament wound around and into each article is plotted and illustratedby the graph of FIG. 30.

Based on the foregoing, it would be expected that articles formed usingthe methods and apparatus of the present invention, together with asimilar mix design and percentage of filaments, would have comparable oreven greater burst strengths compared to the articles formed usingconventional filament winding techniques. The burst strength of articlesformed by the present invention would be expected to be greater becauseof the improved interface between the filaments and the hydraulicallysettable structural matrix resulting from superior compaction,consolidation, and lower porosity of the extruded mixture. Additionally,the articles would be expected to have much better surface qualities asa result of being extruded.

EXAMPLES 317-319

Hydraulically settable articles containing spiral wound filaments wereproduced using the conventional methods of filament winding set forth inExamples 311-316. However, the concentration of filaments was heldconstant at 3.0%, while the winding angle was varied at 35°, 45° and 65°, respectively, in order to determine the effect of the winding angleon the burst strength of the filament wound articles. As shown below,the burst strengths of the articles dramatically increased as thewinding angle was increased.

    ______________________________________                                        Example    Angle         Burst Strength                                       ______________________________________                                        317        35°    10 N/mm.sup.2                                        318        45°    30 N/mm.sup.2                                        319        65°    50 N/mm.sup.2                                        ______________________________________                                    

The burst strengths of the articles as a function of the winding angleof the filaments around the hydraulically settable structural matrix areplotted and illustrated by the graph of FIG. 31.

Based on the foregoing, it would be expected that articles formed usingthe methods and apparatus of the present invention, together with asimilar mix design and percentage of filaments, would have comparable oreven greater burst strengths compared to the articles formed usingconventional filament winding techniques. The burst strength of articlesformed by the present invention would be expected to be greater becauseof the improved interface between the filaments and the hydraulicallysettable structural matrix resulting from superior compaction,consolidation, and lower porosity of the extruded mixture. Additionally,the articles would be expected to have much better surface qualities asa result of being extruded.

EXAMPLES 320-324

Hydraulically settable articles containing spiral wound filaments wereproduced using the conventional methods of filament winding set forth inExamples 311-316. The percentage of filaments wound around and into thehydraulically settable articles was incrementally increased, while thewinding angle was held constant at 45° in order to measure the effect offilament concentration on the modulus of elasticity of the filamentwound articles. As quantified below, the modulus of elasticity showed asignificant and steady increase as the percentage of filaments wasincreased.

    ______________________________________                                        Example   Filament     Modulus of elasticity                                  ______________________________________                                        320       3.0%         1000 N/mm.sup.2                                        321       4.5%         1300 N/mm.sup.2                                        322       6.0%         1600 N/mm.sup.2                                        323       7.5%         2200 N/mm.sup.2                                        324       9.0%         2500 N/mm.sup.2                                        ______________________________________                                    

Plotted and illustrated by the graph of FIG. 32 is the modulus ofelasticity of each article as a function of the percentage of filamentwound around and into the hydraulically settable structural matrix ofeach article.

Based on the foregoing, it would be expected that articles formed usingthe methods and apparatus of the present invention, together with asimilar mix design and percentage of filaments, would have comparable oreven greater modulus of elasticity compared to the articles formed usingconventional filament winding techniques. The modulus of elasticity ofarticles formed by the present invention would be expected to be greaterbecause of the improved interface between the filaments and thehydraulically settable structural matrix resulting from superiorcompaction, consolidation and lower porosity of the extruded mixture.Additionally, the articles would be expected to have much better surfacequalities as a result of being extruded.

EXAMPLES 325-329

Hydraulically settable articles containing spiral wound filaments wereproduced using the conventional methods of filament winding set forth inExamples 311-316. However, the concentration of filaments was heldconstant at 3.0%, while the winding angle was varied at 35°, 45°, 55°,65°, and 75°, respectively, in order to determine the effect of thewinding angle on the modulus of elasticity of the filament woundarticles. As quantified below, the modulus of elasticity of the articlesdramatically increased as the winding angle was increased to about 65°,after which the increase was less dramatic but significant when thewinding angle was increased to 75 °.

    ______________________________________                                        Example  Angle         Modulus of elasticity                                  ______________________________________                                        325      35°     400 N/mm.sup.2                                        326      45°    1200 N/mm.sup.2                                        327      55°    1700 N/mm.sup.2                                        328      65°    2300 N/mm.sup.2                                        329      75°    2600 N/mm.sup.2                                        ______________________________________                                    

Plotted and illustrated by the graph of FIG. 32 is the modulus ofelasticity of each article as a function of the winding angle offilament wound around and into the hydraulically settable structuralmatrix of each article.

Based on the foregoing, it would be expected that articles formed usingthe methods and apparatus of the present invention, together with asimilar mix design and percentage of filaments, would have comparable oreven greater modulus of elasticity compared to the articles formed usingconventional filament winding techniques. The modulus of elasticity ofarticles formed by the present invention would be expected to be greaterbecause of the improved interface between the filaments and thehydraulically settable structural matrix resulting from superiorcompaction, consolidation and lower porosity of the extruded mixture.Additionally, the articles would be expected to have much better surfacequalities as a result of being extruded.

V. SUMMARY.

From the foregoing, it will be appreciated that the present inventionprovides compositions, methods, and apparatus that allow for thesimultaneous placement of filaments during the extrusion ofhydraulically settable materials into articles and shapes which haveheretofore been impossible because of the inherent strength andmoldability limitations of presently known hydraulically settablecompositions.

In addition, the present invention provides compositions, methods, andapparatus for the extrusion of, and placement of filaments within,hydraulically settable articles having an increased tensile strength tocompressive strength ratio compared to conventional hydraulicallysettable materials.

The present invention further provides compositions, methods, andapparatus which result in the ability to continuously extrude, andsimultaneously place filaments within, a hydraulically settable mixturesuch that the extruded article or shape is immediately form stable(i.e., is strong enough to maintain its shape without external support)in the green state upon exiting the extruder die.

The present invention also provides composition, methods, and apparatusthat allow for the continuous placement of filaments having a widevariety of concentrations within an extruding hydraulically settablemixture.

In addition, the present invention provides for the placement ofcontinuous filaments within an extruding hydraulically settable mixtureat a variety of different orientations or angles relative to thelongitudinal axis of the extruded article.

The present invention further provides compositions, methods, andapparatus that yield extruded, form stable pipes and tubes havingsubstantially increased hoop or burst strength.

The present invention also provides compositions, methods, and apparatuswhich result in the effective consolidation or compaction of thehydraulically settable mixture around and through the continuouslyplaced filaments in order to minimize the amount and volume of internalvoids or defects and thereby yield a hardened hydraulically settablestructure matrix that is substantially uniform and of consistently highstrength.

In addition, the present invention provides compositions, methods, andapparatus which yield extruded hydraulically settable articles intowhich filaments have been continuously placed having superior surfaceproperties and greatly reduced surface defects compared to prior artmethods for filament winding cementitious materials.

The present invention further provides compositions, methods, andapparatus that yield a variety of thin-walled hydraulically settablearticles, including articles that require highly critical tolerances ordimensional preciseness.

The present invention also provides compositions, methods, and apparatusthat can be used to extrude, and place continuous filaments within,hydraulically settable articles that can be substituted for articlespresently manufactured from conventional materials such as plastic,clay, metal, or wood.

The present invention additionally provides hydraulically settablecompositions that have a rheology and a plastic-like behavior similar toclay such that such compositions can be extruded using a clay extruder.

Finally, the present invention provides compositions, methods, andapparatus that can be used to continuously manufacture a large varietyof hydraulically settable articles at a cost and at production rates(i.e., high volume or quantity) comparable or even superior to the costof manufacturing such articles from plastic, clay, metal, or wood.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A method for continuously placing filaments within ahydraulically settable mixture being extruded into an article ofmanufacture having a cured hydraulically settable matrix, the methodcomprising the steps of:combining together a hydraulically settablebinder, an aggregate material, a rheology-modifying agent, and water inrelative concentrations to form a hydraulically settable mixture thatflows when extruded under pressure through a die and that is immediatelyform stable upon exiting the die; extruding the hydraulically settablemixture under pressure through a die while continuously placing at leastone filament within the hydraulically settable mixture as the mixture isextruded through the die to form an extruded article having ahydraulically settable matrix that is immediately form stable uponexiting the die and which includes at least one filament placed therein;and allowing the hydraulically settable matrix of the extruded articleto cure to form the article of manufacture having the curedhydraulically settable matrix containing at least one filament.
 2. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 1, wherein the at least onefilament has a generally parallel orientation.
 3. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 1, the die including a longitudinal axis and whereinthe placing step includes winding at least one filament within thehydraulically settable mixture such that the filament has a windingangle greater than about 5° relative to the longitudinal axis of thedie.
 4. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 3, wherein thefilament has a winding angle greater than about 20° relative to thelongitudinal axis of the die.
 5. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim 3,wherein the filament has a winding angle greater than about 35° relativeto the longitudinal axis of the die.
 6. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 3, wherein the filament has a winding angle greater than about 50°relative to the longitudinal axis of the die.
 7. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 3, wherein the filament has a winding angle greaterthan about 75° relative to the longitudinal axis of the die.
 8. A methodfor continuously placing filaments within a hydraulically settablemixture as defined in claim 1, wherein the placing step yields anarticle including filaments having a criss-cross orientation.
 9. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 1, the die including a longitudinalaxis, wherein the placing step yields an article including a filamenthaving a generally parallel orientation and another filament having awinding angle greater than about 5° relative to the longitudinal axis ofthe die.
 10. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 1, wherein thefilament is selected from the group consisting of glass fibers,polyaramide fibers, graphite fibers, carbon fibers, polyethylene fiber,mixtures of the foregoing, and derivatives of the foregoing.
 11. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 1, wherein the hydraulicallysettable binder comprises portland cement.
 12. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 1, wherein the hydraulically settable mixture has an initialdeficiency of water.
 13. A method for continuously placing filamentswithin a hydraulically settable mixture as defined in claim 1, whereinthe hydraulically settable mixture includes a fibrous material.
 14. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 1, wherein the hydraulicallysettable mixture includes a dispersant.
 15. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 1, wherein the article has a cross-section selected from the groupconsisting of circular, rectangular, square, ellipsoidal, andtriangular.
 16. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 1, wherein thearticle comprises a window frame.
 17. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim 1,wherein the article comprises a tubular object.
 18. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 1, wherein the article comprises a sheet.
 19. Amethod for continuously placing filaments within a hydraulicallysettable mixture being extruded into an article of manufacture having acured hydraulically settable matrix, the method comprising the stepsof:combining together a hydraulically settable binder, an aggregatematerial, and water in relative concentrations to form a hydraulicallysettable mixture that flows when extruded under pressure through a dieand that is immediately form stable upon exiting the die; extruding thehydraulically settable mixture under pressure through a die having alongitudinal axis and an interior portion through which the mixturepasses during the extruding step while continuously placing at least onefilament within the hydraulically settable mixture as the mixture isextruded through the interior portion of the die such that the at leastone filament has a winding angle having a magnitude greater than about5° relative to the longitudinal axis to form an extruded article havinga hydraulically settable matrix that is immediately form stable uponexiting the die and which includes at least one filament placed therein;and allowing the hydraulically settable matrix of the extruded articleto cure to form the article of manufacture having a longitudinal axisand comprising the cured hydraulically settable matrix including thefilament with a winding angle having a magnitude greater than about 5degrees relative to the longitudinal axis of the article of manufacture.20. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the combining step isperformed at least in part by means of a high shear mixer.
 21. A methodfor continuously placing filaments within a hydraulically settablemixture as defined in claim 19, wherein the hydraulically settablebinder and aggregate material comprise individual particles having anatural packing density in a range from about 0.65 to about 0.99.
 22. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the hydraulicallysettable binder and aggregate material comprise individual particleshaving a natural packing density in a range from about 0.75 to about0.9.
 23. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 19, wherein thehydraulically settable binder comprises hydraulic cement.
 24. A methodfor continuously placing filaments within a hydraulically settablemixture as defined in claim 23, wherein the hydraulic cement includes aportland cement.
 25. A method for continuously placing filaments withina hydraulically settable mixture as defined in claim 23, wherein thehydraulic cement is selected from the group consisting of microfinecement, slag cement, calcium aluminate cement, plaster, silicate cement,gypsum cement, phosphate cement, white cement, high-alumina cement,magnesium oxychloride cement, aggregates coated with microfine cementparticles, mixtures of the foregoing, and derivatives of the foregoing.26. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the hydraulicallysettable binder comprises fly ash activated with a strong base.
 27. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the combining stepincludes adding a fibrous material to the hydraulically settablemixture.
 28. A method for extruding a hydraulically settable mixture asdefined in claim 27, wherein the fibrous material comprises cellulosicfibers.
 29. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 28, wherein thecellulosic fibers are selected from the group consisting of cotton,bagasse, hemp, abaca, sisal, wood, mixtures of the foregoing, andderivatives of the foregoing.
 30. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim27, wherein the fibrous material comprises fibers selected from thegroup consisting of ceramic fibers, glass fibers, carbon fibers, metalfibers, mixtures of the foregoing, and derivatives of the foregoing. 31.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 27, wherein the fibrous materialcomprises organic polymer fibers.
 32. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim27, wherein the fibrous material has a concentration in a range fromabout 0.5% to about 30% by volume of the hydraulically settable mixture.33. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 27, wherein the fibrous materialhas a concentration in a range from about 1% to about 20% by volume ofthe hydraulically settable mixture.
 34. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the combining step includes adding arheology-modifying agent to the hydraulically settable mixture.
 35. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 34, wherein the rheology-modifyingagent is included in a range from about 0.1% to about 5% by weight ofthe hydraulically settable mixture exclusive of the water.
 36. A methodfor continuously placing filaments within a hydraulically settablemixture as defined in claim 34, wherein the rheology-modifying agent isincluded in a range from about 0.5% to about 1% by weight of thehydraulically settable mixture exclusive of the water.
 37. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 34, wherein the rheology-modifying agent comprises acellulose-based material or a derivative thereof.
 38. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 37, wherein the cellulose-based material is selectedfrom the group consisting of methylhydroxyethylcellulose,hydroxymethylethylcellulose, carboxymethylcellulose, methylcellulose,ethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose,hydroxyethylpropylcellulose, mixtures of the foregoing, and derivativesof the foregoing.
 39. A method for continuously placing filaments withina hydraulically settable mixture as defined in claim 34, wherein therheology-modifying agent comprises a starch-based material or aderivative thereof.
 40. A method for continuously placing filamentswithin a hydraulically settable mixture as defined in claim 30, whereinthe starch-based material is selected from the group consisting ofamylopectin, amylose, sea gel, starch acetates, starch hydroxyethylethers, ionic starches, long-chain alkylstarches, dextrins, aminestarches, phosphate starches, dialdehyde starches, mixtures of theforegoing, and derivatives of the foregoing.
 41. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 34, wherein the rheology-modifying agent comprises aprotein-based material or a derivative thereof.
 42. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 41, wherein the protein-based material is selectedfrom the group consisting of prolamine, collagen derivatives, gelatin,glue, casein, mixtures of the foregoing, and derivatives of theforegoing.
 43. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 34, wherein therheology-modifying agent comprises a synthetic organic material.
 44. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 43, wherein the synthetic organicmaterial is selected from the group consisting of polyvinyl pyrrolidone,polyethylene glycol, polyvinyl alcohol, polyvinylmethyl ether,polyacrylic acids, polyacrylic acid salts, polyvinylacrylic acids,polyvinylacrylic acid salts, polylactic acid, polyacrylimides, ethyleneoxide polymers, latex, mixtures of the foregoing, and derivatives of theforegoing.
 45. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 34, wherein therheology-modifying agent is selected from the group consisting ofalginic acid, phycocolloids, agar, gum arabic, guar gum, locust beangum, gum karaya, gum tragacanth, mixtures of the foregoing, andderivatives of the foregoing.
 46. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the combining step includes adding a dispersant to thehydraulically settable mixture.
 47. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim46, wherein the dispersant is selected from the group consisting ofsulfonated naphthalene-formaldehyde condensate, sulfonatedmelamine-formaldehyde condensate, lignosulfonate, acrylic acid, salts ofthe foregoing, mixtures of the foregoing, and derivatives of theforegoing.
 48. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 19, wherein theaggregate material includes a clay.
 49. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the aggregate material is selected from the groupconsisting of gravel, sand, alumina, silica sand, fused silica, silicafume, fly ash, crushed limestone, crushed sandstone, crushed granite,crushed basalt, crushed bauxite, and mixtures of the foregoing.
 50. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the aggregate materialhas a concentration in a range from about 3% to about 90% by weight ofthe hydraulically settable mixture.
 51. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the aggregate material has a concentration in a rangefrom about 20% to about 70% by weight of the hydraulically settablemixture.
 52. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 19, wherein thehydraulically settable mixture has an initial net deficiency of water.53. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 52, wherein the initial netdeficiency of water is greater than about 10%.
 54. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 52, wherein the initial net deficiency of water isgreater than about 25%.
 55. A method for continuously placing filamentswithin a hydraulically settable mixture as defined in claim 52, whereinthe initial net deficiency of water is greater than about 50%.
 56. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the extruding step isperformed using an auger extruder.
 57. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the extruding step is performed using a piston extruder. 58.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the extruding stepincludes applying a negative pressure to the hydraulically settablemixture in order to remove air from the mixture.
 59. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 19, wherein the extrusion pressure is in a rangefrom about 10 bars to about 7000 bars.
 60. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the extrusion pressure is in a range from about 20bars to about 3000 bars.
 61. A method for continuously placing filamentswithin a hydraulically settable mixture as defined in claim 19, whereinthe extrusion pressure is in a range from about 50 bars to about 200bars.
 62. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 19, wherein theextruding step includes extruding the hydraulically settable mixtureinto a hollow article.
 63. A method for continuously placing filamentswithin a hydraulically settable mixture as defined in claim 62, whereinthe die includes a hollow interior and a mandrel therein to form thehollow article.
 64. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 62, wherein thehollow article has a bulk density up to about 1.5 g/cm³.
 65. A methodfor continuously placing filaments within a hydraulically settablemixture as defined in claim 62, wherein the hollow article has a bulkdensity up to about 0.3 g/cm³.
 66. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim62, wherein the cured hydraulically settable matrix of the hollowarticle of manufacture has a burst strength greater than about 10 N/mm².67. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 62, wherein the cured hydraulicallysettable matrix of the hollow article of manufacture has a burststrength greater than about 30 N/mm².
 68. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 62, wherein the cured hydraulically settable matrix of the hollowarticle of manufacture has a burst strength greater than about 50 N/mm².69. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing stepincludes placing filaments in an amount in a range from about 0.5% toabout 30% by volume of the hydraulically settable mixture.
 70. A methodfor continuously placing filaments within a hydraulically settablemixture as defined in claim 19, wherein the placing step includesplacing filaments in an amount in a range from about 1% to about 20% byvolume of the hydraulically settable mixture.
 71. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 19, wherein the placing step includes placingfilaments in an amount in a range from about 2% to about 10% by volumeof the hydraulically settable mixture.
 72. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the filament is selected from the group consisting ofglass fibers, polyaramide fibers, graphite fibers, carbon fibers,polyethylene fibers, mixtures of the foregoing, and derivatives of theforegoing.
 73. A method for continuously placing filaments within ahydraulically settable mixture as defined in claim 19, wherein thefilament comprises a plurality of individual fibers joined together. 74.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing step yieldsan article including a filament having a winding angle of a magnitudegreater than about 20° relative to the longitudinal axis of the die. 75.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing step yieldsan article including a filament having a winding angle of a magnitudegreater than about 45° relative to the longitudinal axis of the die. 76.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing step yieldsan article including a filament having a winding angle of a magnitudegreater than about 65° relative to the longitudinal axis of the die. 77.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing step yieldsan article including a filament having a winding angle of a magnitudegreater than about 85° relative to the longitudinal axis of the die. 78.A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing step yieldsan article including at least one filament having a winding angle of amagnitude less than about 5° relative to the longitudinal axis of thedie in addition to the at least one filament that has a winding anglehaving a magnitude greater than about 5° relative to the longitudinalaxis of the die.
 79. A method for continuously placing filaments withina hydraulically settable mixture as defined in claim 19, wherein theplacing step yields an article including a filament having a generallyparallel orientation.
 80. A method for continuously placing filamentswithin a hydraulically settable mixture as defined in claim 19, whereinthe placing step yields an article including at least two filamentshaving a criss-cross orientation.
 81. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the placing step includes winding a filament at apredetermined rotational velocity to yield an article having a filamentwith a desired winding angle.
 82. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the extruding step includes extruding the hydraulicallysettable mixture at a predetermined extrusion velocity to yield anarticle having a filament with a desired winding angle.
 83. A method forcontinuously placing filaments within a hydraulically settable mixtureas defined in claim 19, wherein the placing step includes placing apredetermined number of filaments within the hydraulically settablemixture to yield an article having a desired concentration of filaments.84. A method for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 83, wherein the article includes atleast about 10 filaments.
 85. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim83, wherein the article includes at least about 25 filaments.
 86. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 83, wherein the article includes atleast about 50 filaments.
 87. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim83, wherein the article includes at least about 100 filaments.
 88. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing stepincludes placing filaments having a predetermined angle within thehydraulically settable mixture to yield an article having a desiredconcentration of filaments.
 89. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the placing step includes placing filaments having aplurality of predetermined angles within the hydraulically settablemixture to yield an article having desired strength properties.
 90. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the placing stepincludes placing a filament at a predetermined depth within thehydraulically settable mixture.
 91. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the hydraulically settable mixture has a viscositysufficient to reliably draw the filament as the hydraulically settablemixture is extruded through the die.
 92. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the at least one filament has a predetermined tensionto aid in the placement of the filament.
 93. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 92, wherein the predetermined tension of the filament winds thefilament to a desired depth within the hydraulically settable mixture asthe mixture is being extruded.
 94. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the step of allowing the hydraulically settable matrix tocure includes autoclaving the extruded article of manufacture.
 95. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the step of allowingthe hydraulically settable matrix to cure includes placing the extrudedarticle near a source of thermal energy.
 96. A method for continuouslyplacing filaments within a hydraulically settable mixture as defined inclaim 19, wherein the cured hydraulically settable matrix of the articleof manufacture has a tensile strength greater than about 15 MPa.
 97. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the cured hydraulicallysettable matrix of the article of manufacture has a tensile strengthgreater than about 30 MPa.
 98. A method for continuously placingfilaments within a hydraulically settable mixture as defined in claim19, wherein the cured hydraulically settable matrix of the article ofmanufacture has a tensile strength greater than about 50 MPa.
 99. Amethod for continuously placing filaments within a hydraulicallysettable mixture as defined in claim 19, wherein the article comprises apipe.
 100. A method for continuously placing filaments within ahydraulically settable mixture being extruded into an article ofmanufacture comprising a cured hydraulically settable matrix, the methodcomprising the steps of:combining together a hydraulically settablebinder, an aggregate material, a rheology-modifying agent, and water inrelative concentrations to form a hydraulically settable mixture thatflows when extruded under pressure through a die and that is immediatelyform stable upon exiting the die; extruding the hydraulically settablemixture under pressure through a die having a longitudinal axis and aninterior portion through which the mixture passes during the extrudingstep while continuously placing at least one filament within thehydraulically settable mixture as the mixture is extruded through theinterior portion of the die such that the at least one filament has awinding angle having a magnitude greater than about 5° relative to thelongitudinal axis to form an extruded article having a hydraulicallysettable matrix that is immediately form stable upon exiting the die andwhich includes at least one filament placed therein; and allowing thehydraulically settable matrix of the extruded article to cure to formthe cured hydraulically settable matrix of the article of manufacturecomprising the at least one filament.